My message reading Fonts suddenly lost their formatting. In Thunderbird under TOOLS > OPTIONS > DISPLAY > FORMATTING you can change the font, size, and color for reading emails. When I booted up the other day all of the fonts where set back to defaults. All of my settings were still showing but would not respond to any changes I made. I reinstalled Thunderbird which didn't help. I then installed Thunderbird on another Windows 10 PC and had the same problem. I also tried a clean boot. That didn't help either. My version of Thunderbird is 52.5.2. I went back to version 52.5.0. I still had the problem. Any help would be appreciated.