This is probably a issue with the icon cache in your profile. More about profiles: Profiles - Where Firefox stores your bookmarks, passwords and other user data Go to about:profiles and find the profile you are currently using. Open its folder, likely at C:\[Username]\AppData\Roaming\Mozilla\Firefox\Profiles\$$$$$$$$.default, where $ is a random character. (Make sure hidden items are visible in Explorer to access the AppData folder.) Copy the folder somewhere else for backup if you mess up. Delete the corrupted icon cache, which is the file favicons.sqlite in the original profile location.

The cache will be rebuilt once you visit each website. The fastest way is Ctrl+B to open the Bookmarks window, Ctrl+A to select all, right-click the list and click Open all in tabs. The cache should be rebuilt once all websites load. If your bookmarks are arranged in subfolders, right-click each subfolder and click Open all in tabs to open all its contents. If your computer cannot handle that many pages, only select a few at a time by holding Ctrl and clicking them instead of selecting all.

Source: https://support.mozilla.org/en-US/questions/1201268

Hi

This happens if there has been a problem with the favicons.sqlite file in the Firefox profile folder and a new file got created. You will have to visit each bookmark or use an extensions that automates this to reload the favicons from the server.

• Checkmarks https://addons.mozilla.org/firefox/addon/checkmarks-web-ext/

This can be caused by a problem with the places.sqlite and favicons.sqlite databases in the Firefox profile folder.

• use "Verify Integrity" button on the "Help -> Troubleshooting Information" (about:support) page

If errors are reported with "Verify Integrity", close and restart Firefox or reboot and retry.

See also:

• https://support.mozilla.org/en-US/kb/Bookmarks+not+saved#w_fix-the-bookmarks-file
• https://support.mozilla.org/en-US/kb/fix-bookmarks-and-history-will-not-be-functional