Are you using firefox from a new device? Usually if your current browser hasn't been on those website the icons won't load until you visit those specific websites, and then they reside in the cache. Try going to any of your bookmarks and see how the icon shows when the website loads.

If you use Sync then best is to disconnect Sync temporarily during troubleshooting. This could be a problem with the <b>places.sqlite</b> and <b>favicons.sqlite</b> files in the Firefox profile folder. *use the "Places Database" -> "Verify Integrity" button on the "Help -> More Troubleshooting Information" (about:support) page If errors are reported with "Verify Integrity", close and restart Firefox or reboot and retry. If "Verify Integrity" cannot repair places.sqlite, rename/remove all <b>places.sqlite</b> and <b>favicons.sqlite</b> files in the Firefox profile folder with Firefox closed. Firefox will rebuild places.sqlite and restore the bookmarks from the most recent JSON backup in the bookmarkbackups folder. *keep a backup copy of places.sqlite in case a new places.sqlite database has to be created *you lose the history when a new places.sqlite is created You may have to restore an older bookmarks backup in the bookmarkbackups folder via the Bookmarks Manager (Library). *Bookmarks -> Show All Bookmarks -> Import & Backup -> Restore *https://support.mozilla.org/en-US/kb/restore-bookmarks-from-backup-or-move-them See also: *https://support.mozilla.org/en-US/kb/fix-bookmarks-and-history-will-not-be-functional *https://support.mozilla.org/en-US/kb/cant-add-change-or-save-bookmarks You can use the button on the "Help -> More Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the <b>about:profiles</b> page (Root directory). *Help -> More Troubleshooting Information -> Profile Folder/Directory:<br>Windows: Open Folder; Linux: Open Directory; Mac: Show in Finder *https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data