My question is probably simple but I can't find a way to revert it to the previous state.
After installing mscorecofonts (which was installed during pipelight installation) my fonts in Firefox went crazy and it is ugly as hell now.
Can anyone advise how to reset to the "default" font setting?
In my experience ttf-mscorefonts installs broken MS fonts. If I had such an issue as you report, I would go to Firefox > Edit > Prefs > Content > Fonts > Advanced and select there either the Deja Vu or the Liberation font families, both designed for on-screen display.
This should deal with the crazy fonts. If it still doesn't work, you may also experiment with different sizes in that dialogue.
Also see:
