It was pretty nasty, locked up my site for 100's of users on firefox. No issues with other browsers and no issues with previous versions of firefox. I have disabled my viglink addon for now and just starting to investigate. Even after disabling the addon they had to clear cache.
If you run viglink you may want to do some testing. Not sure if anyone else reported this yet or found a fix. I'll likely be contacting viglink soon but am out of office at the moment.