I have used Firefox and kept it updated for years. Today, when I tried to open it, I got this message: Using an older version of Firefox can corrupt bookmarks and browsing history already saved to an existing Firefox profile. To protect your information, create a new profile for this installation of Firefox. Seemed odd, but I created a new profile and synced my bookmarks etc. But when I restarted it, I got the same message. I can't troubleshoot because I can't get past this message. I didn't add anything that I can recall or change any settings, so I don't understand what's going on. Mac ios Montery 12.5.1 edit: moved thread from Firefox for iOS (for iPhone/iPad) to Firefox section as you have <b>macOS</b>.