I had that icon issue for a few weeks, IIRC in Iceweasel beta from mozilla.debian.net . It seems to have resolved itself with d-u/replacement with unstable/main version (not manually, I think unstable just bumped its version number higher) or something I'm not sure of. I didn't do anything directly to resolve it.
Which reminds me I need to d-u. Had internet issues for a couple of weeks so had to wait.