Since you used iceweasel/firefox over several releases, it may be a problem with your profile folder which probably is located in your HOME folder in ~/.mozilla . So first thing to try is a new profile. For that purpose terminate the browser. Make sure, from a terminal, no hidden processes are still running:
ps xuw | grep -E '([i]ceweas|[f]irefox)' should show no process. Then rename the profile folder: mv -i ~/.mozilla ~/.mozilla-prev and start your browser again. Regards, jvp.
