Yesterday I dealt with some issues that were plaguing my cousin’s computer, among which was the odd fact that both MySpace and Yahoo Mail would not allow him to use their sites because his version of Mozilla Firefox was too far out-of-date. The problem was, he was using the most recent version of the program, Firefox 3.5.5, which I confirmed by checking the “About” window under the Help menu in his browser.
Firefox and all other web browsers tell the web pages you visit what browser and version number you are using by sending something called a User Agent string. My suspicion was that Firefox was reporting the wrong User Agent string, and this suspicion turned out to be correct.
First attempt to resolve the issue by turning off or uninstalling your Firefox plug-ins, one-by-one. Chances are, one of your plug-ins corrupting the User Agent string.
If removing plug-ins doesn’t fix the problem you can try to manually check and modify the User Agent settings by typing the address “about:config” into the Firefox address bar and checking the settings under “general.useragent” for an incorrect browser version.