Thunderbird 115: CSS Customization

das10 · Sep 25, 2025

Slightly better. Change the general body color everywhere, then revert it back to original in all the about: tabs (that appears to catch all tabs; only right hand panel of Account Settings tab needs a color to be specified).

Code:

/* userContent.css                                */
/* Change background in messages viewed as "text" */

/* background for general body everywhere */
body  {
   background-color: #ffffe0 ;
}

/* background revert in all about: pages like Settings, Advanced Preferences &c */
/* appears to work on all tabs except right hand panel of "Account Settings"    */
/* tab where it stays as specified above (eg: #ffffe0 )                         */

@-moz-document regexp("about.*") {
   body { 
        background-color: revert ;
   }
}

/* force a background color in right hand side panel of "Account Settings"tab */
#containerBox {
  background-color: #ffffff ;
}

tested: v 143

click click · Sep 25, 2025

Nice. I appreciate you taking the time to bring back soemthing the Mozilla developers should have well enough left alone.

ypain · Oct 13, 2025

Please, help.
I’m trying to create a semi-dark setup by customizing the standard dark theme using userChrome.css. My goal is to have dark menus and folder lists, but keep the message list, message preview pane, and compose window light.

I’ve managed to adjust everything except the message compose window — it stays dark no matter what I try.

das10 · Oct 13, 2025

I presume you are referring to the Message Editor area of the Compose Window (bounded in RED below)? If so, I haven't come across any method of accessing that area through userChrome.css. Perhaps there is some way to do it through a javascript extension - I don't know.

ypain · Oct 13, 2025

das10 said:
I presume you are referring to the Message Editor area of the Compose Window (bounded in RED below)? If so, I haven't come across any method of accessing that area through userChrome.css. Perhaps there is some way to do it through a javascript extension - I don't know.

Yes, I'm speaking about this area.

Thank you!

das10 · Oct 13, 2025

Try this in a userContent.css file (in the same folder as where userChrome.css is).
(Note that with a Dark theme, if you set a light background, then you also need to set a dark color for text as shown in the example.)

userContent.css

Code:

@-moz-document url("about:blank?compose") {
  body {
      background-color: #fffffc  !important;
      color:            #000000  !important;
      } 
}

Chuck99 · Oct 19, 2025

I'm not sure if this is proper thread to ask my question but it does have to do with vers 115 customization.

I recently tried vers 115 but it does not have a Tag with a drop down menu function as shown in this example. This lets you quickly select the importance/color of a message. I tried to customize the Mail Toolbar but was not successful. Not sure which version is shown but you can see the item I'm asking about.

Any suggestions would be appreciated.
Thanks

das10 · Oct 19, 2025

When you right click the tabs bar to customize the toolbar, do you not have this icon in the "Available for Mail Space only" section?

pn: make sure the first tab (called Mail), is selected so you can see the list of the icons/buttons available for the Main Mail Tab.

Chuck99 · Oct 19, 2025

I sure thought I did as you explained & the Tag icon did display on right side of the dotted line that the blue arrow is pointing to. But the icon did not show on the Mail Toolbar.

I thought maybe it was not working because there is a Tag icon already displayed as shown in the example below. Clicking on that displays only messages that have already been tagged.

I’ll have to try it again.

But this makes me wonder, what is the function of the Tag icon that is available for customization? Is it going to duplicate what the existing icon does? Or is it going to also provide a drop down menu?

das10 · Oct 19, 2025

The tag icon you have highlighted in your image, is, as its tooltip suggests to enable you to Filter and "Show only messages with tags on them".
eg: To show all messages which have the Important tag, I would just click on that Tag button (as shown in your image), and then click on the "Any of" dropdown to the left and select the Important button. This is just a simple example of that filter dialog.

The Tag button on the main toolbar is one of the methods to enable you to tag messages (you could also just right click the message of interest & use the tag selector in the context menu, or even go through to the "More" button in the message header & use the Tag selector from there).

Chuck99 · Oct 19, 2025

I know there is a difference between the two. I know I can right click on the message or use the drop down menu from the Message header.

But I would like to be able to have access from the Mail Toolbar as shown. From screenshots I have seen of newer versions this does not exist anymore.
Can this be configured in vers 115 and later?

Ghot · Oct 19, 2025

@Chuck99

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das10 · Oct 19, 2025

I just checked version 115, and the Tags toolbar icon is there (has been there at least from Version 115 to the current version 144 which I showed above). I don't know why it is not appearing for you.

eg: Version 115.8.1

When customizing the toolbar, try placing that icon on the far left of the toolbar to see if it makes any difference.

Chuck99 · Oct 19, 2025

@das10
The vers 115 that I had did not look like yours.
It looked pretty much like this example.

https://blog.thunderbird.net/files/2023/07/115-window-table.png

das10 · Oct 19, 2025

That does look like the same Version 115 I posted the image of, with some Settings changes (eg: If, I "Hide system window titlebar", "hide menubar", select "light theme", and show "Events for the Day-Today Pane").

(Updated image to show the 2 different Tag icons).

Chuck99 · Oct 19, 2025

@das10
Where is the Tags toolbar icon in the vers 115 example I provided? What am I missing?

das10 · Oct 19, 2025

In message #549, you posted an image of Thunderbird. Was that of your own installed version? If so, the tag icon is on the far right of the main toolbar just 'above' the red circle.

Chuck99 · Oct 19, 2025

@das10

That is not my Thunderbird. I just wanted to show my TB had this icon & it was in a cluster with other icons. Clicking on this icon displays messages that have been tagged.

"But this makes me wonder, what is the function of the Tag icon that is available for customization? Is it going to duplicate what the existing icon does? Or is it going to also provide a drop down menu?"

IOW if I'm able to drag & drop the custom Tag icon onto a menu bar, will it give me a drop down menu or just display tagged messages? I don't see an arrow associated with the Custom Tag icon so it makes me question what it does.

I've already restored back to an earlier version of TB & do not have vers 115 currently installed.

That said, the image posted in message #554 is of vers 115 as per the blog link mentioned. It doesn't appear to show a Tag icon with an arrow. That is what I recall mine looked like.

das10 · Oct 19, 2025

The icon on the main toolbar gives you the dropdown as shown in my message #553 so it is not a duplicate of the icon shown in the "Quick Filter" bar.

Chuck99 · Oct 19, 2025

das10 said:
The icon on the main toolbar gives you the dropdown as shown in my message #553 so it is not a duplicate of the icon shown in the "Quick Filter" bar.

Where is that icon shown in message #554?

Thunderbird 115: CSS Customization

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