Here is a quick easy fix for Mozilla Firefox – your bookmark icons (also known as favicons) are kept into a file called favicons.sqlite. Close Firefox, delete the file (or move it to another location), and start Firefox back up.

1. Enter about:support in the location bar
2. Click the Open Profile folder
3. Quit Firefox
4. In the file manager window that opened earlier, delete the favicons.sqlite file (or rename it)

That’s it! My favicons file was 30mb large (I have a lot of bookmarks)