The only time I have seen that happen is when I restored a bookmark backup file. The backup JSON files don't store the favicon data.

Also, the Sync service doesn't synchronize favicon data. So those icons won't appear when new device is being added to the Sync service.

Other than that, the favicons should persist and not disappear.

Do you have any cleanup programs [like CCleaner] running that might be messing with Firefox data files?

You can look at this extension:

• FavIcon Reloader: https://addons.mozilla.org/firefox/addon/faviconreloader/

Tried the add-on and it resulted mostly in messages that told me to "manually add" the icons that were missing. If I knew how to do this, I would have. Please advise.

If the website doesn't provide a favicon then your only option to make one show is to provide a favicon yourself. You can check that by opening the link in a tab and check the favicon on the Tab bar.

Thanks to your helpful responses, I was able to find a solution outside of Firefox, at Google.

This is what worked for me.

https://sites.google.com/site/sonthakit/bookmarkfaviconchanger

Again, thank you for having such a useful forum.