I believe FF 17.0.1 (just updated today) has fixed the Import Images problem, by enabling the Rich Text editor to be used again, as before. Checking by posting an image using html as I used to. If I'm right, this shouldn't be backed up to SF...

... yup, no copy has saved to my SF gallery, just the original imgur pic.
So, not an SF problem at all, but something specific to a version of FF that's now fixed, thankfully.
BTW, looked at the new mobile version a little while ago; very nice, thanks!