Sorry to hear about this problem. You may have more than one version of Firefox installed on your system. The one you used to post this question indicates it is the current 85.0.1 release, so external links may be triggering an older one. Let's try to sort this out. On 64-bit Windows 10, the two most common installation folders for Firefox are: * C:\Program Files\Mozilla Firefox (64-bit programs) * C:\Program Files (x86)\Mozilla Firefox (32-bit programs, 64-bit Firefox after an in-place update from 32-bit) If your shortcut starts one but Windows thinks your default browser is in the other, that can cause this problem. Could you check whether you have two installations? If so, before removing anything, please set your Windows default browser to Internet Explorer or Edge temporarily to avoid possibly breaking programs like Office.