Recently, I have been unable to read text on certain websites. I solved the problem by going to settings, and unckecing "allow websites to choose their own font". This broke google websites icons/buttons. Following that, I disabled all plugins, uninstalled, purged, and reinstalled firefox to the latest version. Created a new clean profile, and nothing works. The problem seems to be upon inspecting the code for gmail messages, "helvetica" is the font listed in the CSS, but I do not have this font installed on my system. I do have an ultra-condensed version which firefox chooses instead of using the font I selected in the settings menu. Activating "troubleshooting mode" solves the problem. But I do not know what troubleshooting mode actually does! There must be more to this mode than removing all plugins and extensions, because I have already tried that. If creating a new clean profile does not solve the problem, there must be some other configuration I am missing. Please advise. Photo attached, Firefox on left, Chrome on right. TL;DR - Firefox chooses the wrong font to display when websites are allowed to choose their own font. Unchecking this box breaks most other websites button/icon control.