Firefox not opening


L

LMWT

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Windows 11
Hello, this is my first post to this forum.

This just happened yesterday, photo attached shows what I get when I attempt to open Firefox browser - it won't! The a small "window" as shown appears when I click on the toolbar icon, but that's it.
This has happened with another program in the past, then I just deleted, reinstalled and all was good.
I would like to fix this rather than delete and reinstall. Just in case, I have imported all my bookmarks to another browser - that worked!
I am using the latest Firefox version.
Can I fix this without deleting and reinstalling (reinstalling over existing doesn't fix it)
If I cannot fix this will finding and copying the correct bookmarks file in the existing program be OK to do? I have looked and there are several files named bookmarks, assume I could save this file and restore it to new copy of Firefox.
Finally slightly off subject, any advise on what's the best browser to use.

Thanks for any help with this.

Firefox.jpg1659699400906.png
 

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First thing to try is to hold down the shift key then try to start Fx; if that works, this method starts Fx in Troubleshooting Mode.
 

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Windows 11 PRO 25H2 (OS Build 26200.6725)Intel Core i7-13700 2.10GHz32 GBNVidia GetForce RTX 4060 Ti
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Windows 11 PRO 25H2 (OS Build 26200.6725)
Computer type
PC/Desktop
Manufacturer/Model
Dell XPS 8960
CPU
Intel Core i7-13700 2.10GHz
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Dell
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32 GB
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NVidia GetForce RTX 4060 Ti
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Realtec
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Dell U2722D
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2560 x 1440
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1024GB SSD boot drive; 2TB Internal Mechanical Hard Disc; WD My Passport (1Tb) external; My Passport Ultra (2Tb) external
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Dell
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MX Master 3
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40Mbps (Bonded DSL)
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Firefox (default)
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Malwarebytes, MS Defender AV
Check if any recent updates and clear cache, that is a good starting point
 

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    Killer E3000 Ethernet Controller
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    Windows 11 Pro10th Gen i-9 10900 K32Gb Dual Channel DDR4 @ 8843MHzNvidia RTX 2080 Super
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Also open Task Manager (Ctrl-Shift-Esc) and make sure that there are no task entries for FF. If there is just end them.
 

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Windows 11 ProIntel Core Ultra16GBIntel(R) Arc Graphics
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Windows 11 Pro
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ASUS Zenbook 14 OLED
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Intel Core Ultra
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16GB
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Intel(R) Arc Graphics
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Realtek High Definition Audio(SST)
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2880 x 1800
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500 GB NVMe SSD
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1,500Mbps
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Firefox, Edge
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Windows Defender
Your profile which has your 'data', bookmarks etc will not be affected by a uninstall/re-install. Just go to add/remove programs of Windows ->settings-> apps remove from there and re-install. Again - your 'profile' will not be affected.

EDIT: Long time user and 14yrs or testing Firefox and use Nightly builds.
 

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Windows 11 Intel i5 10400 HD630 graphics chipi5-1040012 gbHD630 chipset
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Windows 11 Intel i5 10400 HD630 graphics chip
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12 gb
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wireless Logi
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ms 4000 wireless mouse
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10meg
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Win11 Home 25h2 26200.8737 06/23/2026
TheVisitor said:
Your profile which has your 'data', bookmarks etc will not be affected by a uninstall/re-install. Just go to add/remove programs of Windows ->settings-> apps remove from there and re-install. Again - your 'profile' will not be affected.
Click to expand...
Personally I would look for a simple option first, If you don't cure the problem, it could well be there when you reinstall I sure think Quandry's idea is good
 

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    Windows 11 Pro13th Gen Core i9 13900HX32GB DDR5 @4800MHz 2x16GBGeforce RTX 4090HX 16GB
    OS
    Windows 11 Pro
    Computer type
    Laptop
    Manufacturer/Model
    Alienware M18 R1
    CPU
    13th Gen Core i9 13900HX
    Memory
    32GB DDR5 @4800MHz 2x16GB
    Graphics Card(s)
    Geforce RTX 4090HX 16GB
    Sound Card
    Nvidia HD / Realtek ALC3254
    Monitor(s) Displays
    18" QHD+
    Screen Resolution
    25660 X 1600
    Hard Drives
    C: KIOXIA (Toshiba) 2TB KXG80ZNV2T04 NVMe PCIe M.2 SSD
    D: KIOXIA (Toshiba) 2TB KXG80ZNV2T04 NVMe PCIe M.2 SSD
    Case
    Dark Metallic Moon
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    Alienware M Series per-key AlienFX RGB
    Mouse
    Alienware AW610M
    Browser
    Chrome and Firefox
    Antivirus
    Norton
    Other Info
    Killer E3000 Ethernet Controller
    Killer Killer AX1690 Wi-Fi Network Adaptor Wi-Fi 6E
    Bluetooth 5.2
    Alienware Z01G Graphic Amplifier

  • At a glance

    Windows 11 Pro10th Gen i-9 10900 K32Gb Dual Channel DDR4 @ 8843MHzNvidia RTX 2080 Super
    Operating System
    Windows 11 Pro
    Computer type
    Laptop
    Manufacturer/Model
    Alienware Area 51m R2
    CPU
    10th Gen i-9 10900 K
    Memory
    32Gb Dual Channel DDR4 @ 8843MHz
    Graphics card(s)
    Nvidia RTX 2080 Super
    Sound Card
    Nvidia
    Screen Resolution
    1920 x 1080
    Hard Drives
    Hard Drive C: Samsung 2TB SSD PM981a NVMe
    Hard Drive D:Samsung 2TB SSD 970 EVO Plus
    Mouse
    Alienware 610M
    Browser
    Chrome
    Antivirus
    Norton
What I see on that image is that Firefox is open but in a reduced window size. Move the mouse pointer to an edge and see if it can be resized or press the middle icon in the upper right corner to Restore or Maximize. Also could try F11 to go to Full Screen [Yes, that is different from Maximized]. An open program shows a line under the icon for it on the Taskbar.
 

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  • At a glance

    Win11 Pro RTM Version 24H2 Build 26100.4202Intel Core i5 11th Gen. 2.40GHz12GB
    OS
    Win11 Pro RTM Version 24H2 Build 26100.4202
    Computer type
    Laptop
    Manufacturer/Model
    Dell Vostro 3400
    CPU
    Intel Core i5 11th Gen. 2.40GHz
    Memory
    12GB
    Hard Drives
    256GB SSD NVMe M.2

  • At a glance

    Win11 Pro RTM Version 24H2 Build 26100.4202Intel Core i5 10th Gen. 2.90GHz16GBOnboard, no VGA, using a DisplayPort-to-VGA a...
    Operating System
    Win11 Pro RTM Version 24H2 Build 26100.4202
    Computer type
    PC/Desktop
    Manufacturer/Model
    Dell Vostro 5890
    CPU
    Intel Core i5 10th Gen. 2.90GHz
    Memory
    16GB
    Graphics card(s)
    Onboard, no VGA, using a DisplayPort-to-VGA adapter
    Monitor(s) Displays
    24" Dell
    Hard Drives
    512GB SSD NVMe, 4TB Seagate HDD
    Browser
    Firefox, Edge
    Antivirus
    Windows Defender/Microsoft Security
i did have a similar issue awhile back. it wasnt firefox for me it was related to a windows update. Did it work for you say last week? can you check your windows updates and see if you had one recently as in this week and I would uninstall it. then reboot and see what happens. Many of my apps were doing a weird thing where i would open it and it would be downsized like that, id click on the taskbar icon and it would open but then i couldnt close the window. the only way i could close anything was to go into task manager and find the process and close it that way..talk about crazy irritating headache.
 

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Windows 11 Pro Version 23H2(OS Build 22631.4890)
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AMD
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12-Core AMD Ryzen 9 5900X, 4950 MHz (49.5 x 100)
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logitech
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logitech
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1 GB
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Eset Endpoint Security
LMWT said:
a small "window" as shown appears when I click on the toolbar icon, but that's it.
Click to expand...
Sometimes the coordinates for an app's window's size and position can get corrupted. Your little 'windows' shows Firefox is obviously working, it has a web page showing. But when you click on it the full size window is probably trying to display somewhere off the edge of your screen.

Changing your display resolution to something smaller, then back to normal again, may reset the window's coordinates.

You could also try right-clicking on the little window and selecting Maximise.

1659715519285.png
 

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System One System Two Other systems

  • At a glance

    Windows 11 HomeAMD Athlon Silver 3050U8GBRadeon Graphics
    OS
    Windows 11 Home
    Computer type
    Laptop
    Manufacturer/Model
    Acer Aspire 3 A315-23-R9VY
    CPU
    AMD Athlon Silver 3050U
    Memory
    8GB
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    Radeon Graphics
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    laptop screen
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    1366x768 native resolution, up to 2560x1440 with Radeon Virtual Super Resolution
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    1TB Samsung EVO 870 SSD (from April 2026: 250GB EVO 850)
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    150 Mbps
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    Edge, Firefox
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    Defender
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    fully 'Windows 11 ready' laptop. Windows 10 C: partition migrated from my old unsupported 'main machine' then upgraded to 11. A test migration ran Insider builds for 2 months. When 11 was released on 5th October 2021 it was re-imaged back to 10 and was offered the upgrade in Windows Update on 20th October. Windows Update offered the 22H2 Feature Update on 20th September 2022. It got the 23H2 Feature Update on 4th November 2023 through Windows Update, 24H2 on 3rd October 2024 through Windows Update by setting the Target Release Version for 24H2, and 25H2 on 30th September 2025 through Windows Update by setting the Target Release Version for 25H2.

    UPDATE - 11 April 2026: due to mechanical deterioration this PC has been retired from active duty. The OS with all software and files has been migrated to my System Seven in 'Other systems' to carry on as my general purpose 'main machine'.

  • At a glance

    Windows 11 ProIntel® Core™ i5-520M8GB(integrated graphics) Intel HD Graphics
    Operating System
    Windows 11 Pro
    Computer type
    Laptop
    Manufacturer/Model
    Dell Latitude E4310
    CPU
    Intel® Core™ i5-520M
    Motherboard
    0T6M8G
    Memory
    8GB
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    (integrated graphics) Intel HD Graphics
    Screen Resolution
    1366x768
    Hard Drives
    500GB Crucial MX500 SSD
    Browser
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    Antivirus
    Defender
    Other Info
    unsupported machine: Legacy bios, MBR, TPM 1.2, upgraded from W10 to W11 using W10/W11 hybrid install media workaround.

    In-place upgrade to 22H2 using ISO and a workaround.
    Feature Update to 23H2 by manually installing the Enablement Package.
    In-place upgrade to 24H2 using hybrid 23H2/24H2 install media.
    Upgraded to 25H2 by Enablement Package.

    Also running Insider Dev, and Canary builds and Windows 10 as native boot .vhdx.
  • My SYSTEM THREE is a Dell Latitude 5410, i7-10610U, 32GB RAM, 512GB NVMe ssd, supported device running Windows 11 Pro.

    My SYSTEM FOUR is a 2-in-1 convertible Lenovo Yoga 11e 20DA, Celeron N2930, 8GB RAM, 256GB ssd. Unsupported device: currently running Win10 Pro, plus Win11 Pro RTM and Insider Dev, Beta, and RP 24H2 as native boot vhdx.

    My SYSTEM FIVE is a Dell Latitude 3190 2-in-1, Pentium Silver N5030, 8GB RAM, 1TB NVMe ssd, supported device running Windows 11 Pro, plus Insider Beta, Dev, and Canary builds (and a few others) as a native boot .vhdx.

    My SYSTEM SIX is a Dell Latitude 5550, Core Ultra 7 165H, 64GB RAM, 1TB NVMe SSD, supported device, Windows 11 Pro 24H2, Hyper-V host machine. Updated to 25H2 on 30th September 2025.

    My SYSTEM SEVEN is a Lenovo Thinkpad T580, Intel Core i7-8650U, 16GB RAM, 512GB NVMe SSD + 2nd 512GB NVMe SSD, a supported device for Windows 11. This is my current general purpose 'main machine'. The installed Windows 11 Home from my System One has been migrated to this machine.
Not Myself said:
First thing to try is to hold down the shift key then try to start Fx; if that works, this method starts Fx in Troubleshooting Mode.
Click to expand...
Thank you all so much for the great replies,

I decided I would start with the first reply from Not Myself and so happy, problem solved - shift key + Open Fx
I normally use one click to open things, so initially thought this wasn't going to work, did a double click and choose to refresh Fx..................

Refresh Firefox 1.jpgRefresh Firefox 2.jpgRefresh Firefox 3.jpg
All good now, just have to restore some customizations and a few extensions
 

My Computer My Computer

At a glance

Windows 11
OS
Windows 11
Computer type
PC/Desktop
Manufacturer/Model
Dell Inspiron 3881
Hard Drives
SSD and HDD
Bree said:
Sometimes the coordinates for an app's window's size and position can get corrupted. Your little 'windows' shows Firefox is obviously working, it has a web page showing. But when you click on it the full size window is probably trying to display somewhere off the edge of your screen.

Changing your display resolution to something smaller, then back to normal again, may reset the window's coordinates.

You could also try right-clicking on the little window and selecting Maximise.

View attachment 35695
Click to expand...
Thank you for the reply,

Tried maximise before posting the thread with no success.
 

My Computer My Computer

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Windows 11
OS
Windows 11
Computer type
PC/Desktop
Manufacturer/Model
Dell Inspiron 3881
Hard Drives
SSD and HDD
Berton said:
What I see on that image is that Firefox is open but in a reduced window size. Move the mouse pointer to an edge and see if it can be resized or press the middle icon in the upper right corner to Restore or Maximize. Also could try F11 to go to Full Screen [Yes, that is different from Maximized]. An open program shows a line under the icon for it on the Taskbar.
Click to expand...
Thank you Berton,

Before posting the query, did try what you wrote but not F11!
 

My Computer My Computer

At a glance

Windows 11
OS
Windows 11
Computer type
PC/Desktop
Manufacturer/Model
Dell Inspiron 3881
Hard Drives
SSD and HDD
I frequently use F11 when trying to view items that are just a bit too big for the Maximized program.
 

My Computers My Computers

System One System Two

  • At a glance

    Win11 Pro RTM Version 24H2 Build 26100.4202Intel Core i5 11th Gen. 2.40GHz12GB
    OS
    Win11 Pro RTM Version 24H2 Build 26100.4202
    Computer type
    Laptop
    Manufacturer/Model
    Dell Vostro 3400
    CPU
    Intel Core i5 11th Gen. 2.40GHz
    Memory
    12GB
    Hard Drives
    256GB SSD NVMe M.2

  • At a glance

    Win11 Pro RTM Version 24H2 Build 26100.4202Intel Core i5 10th Gen. 2.90GHz16GBOnboard, no VGA, using a DisplayPort-to-VGA a...
    Operating System
    Win11 Pro RTM Version 24H2 Build 26100.4202
    Computer type
    PC/Desktop
    Manufacturer/Model
    Dell Vostro 5890
    CPU
    Intel Core i5 10th Gen. 2.90GHz
    Memory
    16GB
    Graphics card(s)
    Onboard, no VGA, using a DisplayPort-to-VGA adapter
    Monitor(s) Displays
    24" Dell
    Hard Drives
    512GB SSD NVMe, 4TB Seagate HDD
    Browser
    Firefox, Edge
    Antivirus
    Windows Defender/Microsoft Security
The-Hive said:
Check if any recent updates and clear cache, that is a good starting point
Click to expand...
Thanks The-Hive,

I did those but it didn't help.
 

My Computer My Computer

At a glance

Windows 11
OS
Windows 11
Computer type
PC/Desktop
Manufacturer/Model
Dell Inspiron 3881
Hard Drives
SSD and HDD
Quandary said:
Also open Task Manager (Ctrl-Shift-Esc) and make sure that there are no task entries for FF. If there is just end them.
Click to expand...
Hi Quandary,

Tried that, didn't solve the problem.
 

My Computer My Computer

At a glance

Windows 11
OS
Windows 11
Computer type
PC/Desktop
Manufacturer/Model
Dell Inspiron 3881
Hard Drives
SSD and HDD
TheVisitor said:
Your profile which has your 'data', bookmarks etc will not be affected by a uninstall/re-install. Just go to add/remove programs of Windows ->settings-> apps remove from there and re-install. Again - your 'profile' will not be affected.

EDIT: Long time user and 14yrs or testing Firefox and use Nightly builds.
Click to expand...
Thanks TheVisitor,

That's the one I was a bit cautious about doing, but good advice for the future!
 

My Computer My Computer

At a glance

Windows 11
OS
Windows 11
Computer type
PC/Desktop
Manufacturer/Model
Dell Inspiron 3881
Hard Drives
SSD and HDD
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