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What about:config parameter will adjust the font size for *only* tabs and toolbar text?

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What configuration setting do I adjust if I want to change the font size of only the tabs and toolbar text, not the text of the window / body (managed with Windows' "Make text bigger" option)? I've made the text of the tabs and toolbar large enough for my taste, yet that same setting make the text for everything else in the browser way too big. I'd rather not download a third-party extension as the solution as that implies third-party data gathering. Thank you.

What configuration setting do I adjust if I want to change the font size of only the tabs and toolbar text, not the text of the window / body (managed with Windows' "Make text bigger" option)? I've made the text of the tabs and toolbar large enough for my taste, yet that same setting make the text for everything else in the browser way too big. I'd rather not download a third-party extension as the solution as that implies third-party data gathering. Thank you.

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Note that Firefox has a Zoom section in Settings to set the default zoom level for webpages.

  • Settings -> General -> Language and Appearance -> Zoom

To make adjustments to the font size only for specific places like the tab bar and other toolbars, you need to CSS code in userChrome.css.

Add CSS code to the userChrome.css file in the chrome folder in the Firefox profile folder.


#navigator-toolbox * {font-size: 12pt !important}

It is not that difficult to create userChrome.css if you have never used it.

The first step is to open the "Help -> Troubleshooting Information" page and find the button to access the profile folder with the random name (xxxxxxxx.default-release).

You can find the button to go to the profile folder under the "Application Basics" section as "Profile Folder -> Open Folder". If you click this button then you open the profile folder in the Windows File Explorer. You need to create a folder with the name chrome in the profile folder with the random name (name is all lowercase). In the chrome folder you need to create a plain text file with the name userChrome.css (name is case sensitive). In this userChrome.css text file you paste the text posted. On Mac you can use the TextEdit utility to create the userChrome.css file as a plain text file.

In Windows saving the file is usually the only time things get more complicated because Windows can silently add a .txt file extension and you end up with a file named userChrome.css.txt. To avoid this you need to make sure to select "All files" in the dialog to save the file in the text editor using "Save File as".

You need to close (Quit/Exit) and restart Firefox when you create or modify the userChrome.css file.

More info about userChrome.css/userContent.css in case you are not familiar: *https://www.userchrome.org/what-is-userchrome-css.html

In Firefox 69 and later you need to set this pref to true on the about:config page to enable userChrome.css and userContent.css in the chrome folder.

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I can't believe it's so difficult to do this --- especially since my tab font sizes were fine until I updated to the latest version of Firefox.