Recently I installed Firefox 40.0.3 on a new system. I copied my old user profile (created under an earlier version of FF) and so far everything works.

However, in my old profile, there are lots of custom font settings that doesn't make sense for the new system (changed font names, different display, hence different optimal font size for my eyes, and different locales). I'd like to remove all settings related to the fonts and use whatever should haven there by default had I not copied my old profile. For everything else in my user profile, I'd like to keep them.

Is there a quick method to do this, instead of reverting all font settings for all locales one by one?

Edit: for now, I've accepted my own answer, because that's what I've tried and what I have experience with. I'm still seeking the answer to the original question: How to programmatically, or automatically revert a certain selection of config options to their default values? In particular, how to restore all font settings? Feel free to discuss ;)

  • Have you looked at here to copy just the specific things you want instead of the whole profile? – Unfundednut Sep 19 '15 at 13:36
  • @MrStatic, yes, I've read that, but it doesn't seem to address the problem with fonts. Basically, I just cp'ed my whole old profile and chose that as default in profile manager. It works without any problem, except this one. – user319088 Sep 19 '15 at 13:39

Well I ended up searching for the string font in about:config and reset all user-set options. It was a grind but I'm a cheap labor anyway ;)

But I'm sure there are better methods to do this. Perhaps someone with more experience on Firefox internal could enlighten me on how to do this programmatically.


The Mozilla Support Forum thread Web page font issues has this advice :

The Reset Firefox feature can fix many issues by restoring Firefox to its factory default state while saving your essential information. Note: This will cause you to lose any Extensions and some Preferences.

  1. Click the menu button image1, click Help image2 and select Troubleshooting Information. A new tab containing your troubleshooting information should open.
  2. At the top right corner of the page, you should see a button that says "Reset Firefox" image3. Click on it.
  3. Firefox will close and reset. After Firefox is done, it will show a window with the information that is imported. Click Finish.
  4. Firefox will open with all factory defaults applied.


  • 1
    Hi, I ended up doing something very similar, but manually. I just reset the font settings one-by-one in about:config. – user319088 Sep 19 '15 at 18:07

have you tried changing the default font settings in firefox

  1. Remove custom font files from your firefox user profile folder
  2. Go to "about:preferences#content"
  3. change Default font to "Times New Roman"
  4. change Size to "16"
  5. click on Advanced on use the following values
    • Fonts for : Latin
    • Proportional : Serif & Size : 16
    • Serif : Times New Roman
    • Sans Serif : Arial
    • Monospace : Courier New & Size :13
    • Minimum font size : 9
    • Fallback Text Encoding : Default for Current Locale
  6. Restart Firefox

if this still doesn't work - try resetting about:config preferences as suggested by user "Cong Ma"

Screenshot of Fonts & Colours setting in about:preferences#content


Screenshot of Advanced font settings in about:preferences#content


  • I basically did this, but from about:config page, which is faster to operate by hand ;) due to less amount of cursor-moving. – user319088 Sep 21 '15 at 11:40
  • using about:config comes with some risk. what happened after you tried this? (before using about:config page) – xypha Sep 21 '15 at 11:44
  • I decided the risk worth taking because all my profiles are backed-up. What "happened" was the reversion to default of all font settings, with no known adverse side-effect. Also I edit about:config fairly regularly, and although I'm no expert, I kinda understand what kind of options are better off left to default. – user319088 Sep 21 '15 at 11:55
  • Just like to add to this that "Allow pages to choose their own fonts, instead of my selections above" is ticked per default Firefox settings. Not sure if for you, @CongMa, this is also related to the fonts. – lowtechsun Nov 3 '16 at 21:06

You may use MozBackup to do this. Backup all the needed things from the profile and then restore it from the backup.

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