Hi Susan,
Thanks for your post. Apart from verifying the App default, please also verify the browser isn't overriding the OS.
For Edge open Settings > Cookies and site permissions > Protocol handlers. Under Handlers for email links, click the 3 dot (...) menu and remove any "Default" entry that's not Outlook. The steps will be similar for Chrome/Firefox/Safari, Google for the instructions if needed.
Also, if you select the Firefox program to handle a file when you get an "Open with" dialog.
Check the Mailto application in Firefox > Preferences > Applications Make sure it isn't set to the Firefox application because Firefox can't handle the mailto protocol internally and you will get tabs opening endlessly.
Best Regards,
Ian Xue
If the Answer is helpful, please click "Accept Answer" and upvote it.