specifically, quickbooks online and facebook
Hello katpollock. Your user agent is corrupted by Fast Browser Search (FBSMTWB) and that identifies you as Firefox/3.6.8
see your user agent:
Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:126.96.36.199) Gecko/20100722 Firefox/3.6.8 GTB7.1 ( .NET CLR 3.5.30729) FBSMTWB
in the next link see how to reset user agent : Websites say that Firefox is outdated or incompatible even though it's the latest version
see also the next page about Fast Browser Search (FBSMTWB in the user agent).
Please mark "Solved" the answer that really solve the problem, to help others with a similar problem.
hello katpollock, apparently firefox is reporting a wrong user agent to websites & identifies itself as firefox 3.6.8 - please reset the user agent string as it is described in the following support article: Websites say that Firefox is outdated or incompatible even though it's the latest version
please also uninstall any toolbars you don't need since they can cause additional problems: Remove a toolbar that has taken over your Firefox search or home page