Bookmark folder icons disappeared.
I can not restore them. The "Change Favicon" option has disappeared too.
Can you try to start Firefox in Safe Mode to see if Firefox works properly with no error? You can start Firefox in Safe Mode below:
- Windows/Mac: Go to Help > Restart with add-ons disabled
- Linux: Run firefox -safe-mode in the Terminal/Konsole
If Firefox opens up fine with no problems, it's probably one of your extensions that's causing the issue. You can re-enable your add-ons one by one until you find the one that causes the issue upon being re-enabled.