You could always decide to go for Firefox Portable with Narsil and run multiple instances of that, in parallel (with the AllowMultipleInstances=true in FirefoxPortable.ini in the same folder as the .exe) via multiple sandboxes in Sandboxie-Plus. By making multiple copies of the same FirefoxPortable folder, it becomes possible (and easy) to configure each copy individually, and, by making multiple Sandboxie-Plus sandboxes in addition to this, it also becomes possible (and easy) to configure each sandbox individually. Neither one of both these two options will prevent you from still
also using Firefox profiles and the Multi-Account Containers addon, uBlock Origin, etc. so, it is a really very powerful strategy to consider.
Further, if you also set the sandbox location of some of your sandboxes to a folder on a ramdisk (I use Romex Primo Ramdisk with Dynamic Memory Management in Compact Mode, mainly for this purpose), you can boost it significantly, e.g. by writing your own automation scripts that let you be in control of what data gets stored on the ramdisk, of when that data gets stored on the ramdisk, and of when that data gets deleted from the ramdisk. Another reason why I prefer to use the Portable edition of Firefox is that any copy of the FirefoxPortable folder can easily be copied again, to any location on the SSD or on the ramdisk, inside or outside a sandbox. And I can make differential copies with a copy tool like FastCopy, also via a script and whenever I want.
Finally, Sandboxie-Plus can also save on storage space, as it doesn't populate a sandbox with a file before the file gets modified by a sandboxed process that runs in that sandbox. One implication of this is that you also get to choose between letting Sandboxie-Plus copy the file to the sandbox as a result of such a modification when it happens or letting your script [that you wrote yourself] that you've got running outside the sandbox copy the file to the sandbox when your script decides to do so. That is, also in addition to letting yourself be in control of when to delete or move certain files out of the sandbox. Heck, with such a browsing station you could actually even set it up such a way that it collects pr0n in copious amounts from Titter (I know it's now called X, but I still prefer to call it Titter... just because I can) uninterruptedly all night so it feeds all the resulting privacy metadata to Alphabet Inc. and lord knows who else.
Then see how much they like to steal your data.
