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How do I change the font size of Firefox's headers elements: menu, tabs, bookmark toolbar, bookmark manager without changing the font across Mac iOS or otherwise messing up the other settings?

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How do I change the font size of Firefox's headers elements: menu, tabs, bookmark toolbar, bookmark manager without changing the font across Mac iOS or otherwise messing up the other settings?

I've searched this question and found one answer archived that did not really fix the problem. I'm looking for an extension or a setting integrated in FF, not a font size change in Mac iOS (Monterey) or one that changes the font in the browser pages.

Love FF and Mozilla and all the volunteers who make my entire work day so easy with great, secure, handsome products! I'm a devoted fan. Thank you!

How do I change the font size of Firefox's headers elements: menu, tabs, bookmark toolbar, bookmark manager without changing the font across Mac iOS or otherwise messing up the other settings? I've searched this question and found one answer archived that did not really fix the problem. I'm looking for an extension or a setting integrated in FF, not a font size change in Mac iOS (Monterey) or one that changes the font in the browser pages. Love FF and Mozilla and all the volunteers who make my entire work day so easy with great, secure, handsome products! I'm a devoted fan. Thank you!

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There is a preference layout.css.devPixelsPerPx which you will find by searching for Pixels in about:config. https://support.mozilla.org/en-US/questions/1327127

If that doesn't achieve what you want, you can create a file userChrome.css.

Modified by Terry

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You can set layout.css.devPixelsPerPx to 1.0 (default is -1) on the about:config page. Adjust its value in 0.1 or 0.05 steps (1.1 to enlarge or 0.9 to reduce) until icons or text looks right. Make sure not to use values too large or too small.

  • modifying layout.css.devPixelsPerPx affects user interface and webpages (global zoom)

Firefox has a Zoom section in Settings to set the default zoom level for webpages, so you can use that to revert the changes caused by layout.css.devPixelsPerPx.

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

You can open the about:config page via the location/address bar. You can click the button to "Accept the Risk and Continue".