Firefox Increase gui font size

12. 7. 2025

About Mozilla Firefox ↓

shows version: 140.0.4 (64-bit)

Where is my profile fodler ↓

Got to about:support and find ‘Profile folder’

Open it and add fodler named ‘chrome’, add userChrome.css in it. For example this one:
https://raw.githubusercontent.com/brontosaurusrex/stretchbang/master/.mozilla/firefox/userChrome.css

Enable stuff in about.config, making ‘toolkit.legacyUserProfileCustomizations.stylesheets’ true.

Increase the gui font? ↓

Add

/* Increase gui font */
* {
  font-size: 10pt !important;
}

to the userChrome.css.

Restart firefox, profit. Tabs should be curved a little and font should be bigger. This should NOT affect the web zoom / size of the web pages.

Btw ↓

You can also change the font

/* Increase gui font */
* {
font-family: "3270 Nerd Font", sans-serif !important;
font-size: 13pt !important;
}

Full userChrome.css example ↓

/* put me in ~/.mozilla/firefox/_yourprofile_/chrome/userChrome.css */
/* https://brontosaurusrex.github.io/2018/09/08/firefox-quantum/ */

@namespace url(http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul);

/* Give me some curves */
.tab-background {
border-radius: 10px 10px 2px 2px !important;
border-image: none !important;
}
.tab-line {
display: none;
}

/* remove colored line above each tab */
#TabsToolbar .tabbrowser-tab .tab-line {
    visibility: hidden;
}

/* Don't show close button until hovered https://www.reddit.com/r/firefox/comments/731vz1/userchromecss_hack_for_showing_close_button_on/ */
.tabbrowser-tab:not(:hover) .tab-close-button{ display:none; }
.tabbrowser-tab:not([pinned]):hover .tab-close-button{ display:block !important; }

/* Remove separator between tabs */
.tabbrowser-tab::before, 
.tabbrowser-tab::after{
display: none !important;
}

/* Increase gui font */
* {
font-size: 10pt !important;
}

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