Internet Explorer is the only program on my computer that can access the internet

From one day to the next, the only program that can access the internet is Internet Explorer. I do not use it otherwise, I only use Firefox. Thunderbird can no longer access the internet, AVG can't, only Internet Explorer. From a command prompt I can ping my router, Google and other internet sites, so my hardware is fine. Any help would be appreciated == This happened == Every time Firefox opened == From one day to the next == == User Agent == Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1; Win64; x64; Trident/4.0; .NET CLR 2.0.50727; SLCC2; .NET CLR 3.5.30729; .NET CLR 3.0.30729; .NET4.0C)