Every website seems to think I'm running 3.0.15, but I've downloaded the new 5.0.1 and the about firefox says I'm running 5.0.1.
All my plugins are up to date. When I go to Mozilla's home page a fuzzy monster tells me, "Hey there! Looks like you’re using an old version of Firefox." Many websites tell me they do not support my old version. Programs and Features lists me as having 5.0.1 installed also and there is not a second instance of firefox installed.
Alla svar (1)
Your UserAgent string in Firefox is messed up by another program that you installed.
http://en.wikipedia.org/wiki/User_Agent
type about:config in the URL bar and hit Enter
If you see the warning, you can confirm that you want to access that page.
Filter = general.useragent.
Right-click the preferences that are bold, one line at a time, and select Reset.
Then restart Firefox