If using a custom background image, it will disappear upon restarting Firefox.
Upon restoring a backup speed dial, all dials came back as blanks, without their associated images.
Did you have custom images, from gallery or auto-generated?
Did you Clean Cookies or Cache?
Also, extensions like CCleaners clean it and break. Do you use cleaners?
I don't use cleaners.
Images for the tabs are selected from the custom option available in edit tab. (And btw, it is impossible to do so for a tab associated to google.com, which is definitely not normal.)
Just to avoid wasting time: nothing changed in my PC except the Speed Dial update.
Please contact us email@example.com and mention this topic.
Our developer will make a teamview with you to solve the problem
Customer support service by UserEcho