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 ;)