If you want, you can have more than one Firefox version on your system. Do you want to get rid of the older ones? Let’s do a full clean re-install; [http://www.mozilla.org/en-US/firefox/all/ Download Firefox For All languages And Systems] {web link} Save the file. Then '''Close Firefox. ''' Using your file browser, open the '''Programs Folder''' on your computer. '''Windows: ''' C:\Program Files C:\Program Files (x86) '''Note:''' Check Both Folders '''Mac: ''' Open the ''' "Applications" ''' folder. https://support.mozilla.org/en-US/kb/how-download-and-install-firefox-mac '''Linux: ''' Check your user manual. If you installed Firefox with the distro-based package manager, you should use the same way to uninstall it. See Install Firefox on Linux; https://support.mozilla.org/en-US/kb/install-firefox-linux If you downloaded and installed the binary package from the Firefox download page, simply remove the folder Firefox in your home directory. http://www.mozilla.org/firefox#desktop ++++++++++++++++++++++++++++ Look for, and remove any '''Mozilla''' or '''Firefox''' program folders. Do not remove the '''Mozilla Thunderbird''' folder if there is one. '''Do Not''' remove any profile folders. After rebooting the computer, run a registry scanner if you have one. Then run the installer. +++++++++++++++++++++++++++ If there is a problem, start your '''Computer''' in safe mode and try again. http://encyclopedia2.thefreedictionary.com/Linux+Safe+Mode This shows how to Start all Computers in Safe Mode; Free Online Encyclopedia

If you switch between a 32-bit and a 64-bit Firefox version then the user agent changes. It is possible that only one specific user agent disables the 2FA dialog. ---- You may want to keep only one Firefox version and remove.uninstall the other. *(64-bit Firefox) "C:\Program Files\Mozilla Firefox\" *(32-bit Firefox) "C:\Program Files (x86)\Mozilla Firefox\"