I'm guessing this might be related to the FF Image Gallery issue, but if not:

Animated icons are no longer animated in FF.  (Working normally in MEF.)  They appear animated in the menu but in messages are fixed with a black background.  Non-animated icons are also surrounded by a black background.  This applies only to icons in the Vault, not the ones in the quickie menu under the "smilie face."  First noticed Sunday evening, they were okay Sunday morning.