https://support.mozilla.org/en-US/questions/1207775 https://support.mozilla.org/en-US/questions/1208759#answer-1086882 https://support.mozilla.org/en-US/kb/how-change-your-default-browser-windows-10 https://www.bing.com/search?q=change+default+browser+windows+10

Some users had this issue after the Windows 10 Microsoft Edge update. If you reinstall Firefox, it should reappear on the list of browsers. If it doesn't, there's a manual way to add it, but generally it will come back if you reinstall. You shouldn't lose any Firefox data, but it's always best to [[Back up and restore information in Firefox profiles|back up your data]] <u>'''BEFORE'''</u> reinstalling Firefox, just to be on the safe side. If your data (bookmarks, etc) doesn't appear in Firefox after reinstalling, the [[Recover user data missing after Firefox update]] will have the steps you need to fix it. Hope this helps.