I find that recent versions of Iceweasel (10 & 11) crash when I try to visit certain websites. I'm fairly sure that some issue with the Flash plugin is to blame, as sometimes the website opens OK if I whitelist it in my Flashblock preferences; but this doesn't always work. As far as I know, the installed Flash version is compatible with my system. I didn't get this problem with Iceweasel 9, which is no longer available in the repositories so I can't revert to it now.
Edit: Things improve when I re-enable the Firefox/Iceweasel plugin-container, which prevents the whole browser crashing if there is a problem with one or more plugins. I had disabled the container as it runs in a separate process, using quite a lot of extra memory.