Making EMClient the default app for email

I have set emclient as default app in Wndows settings but when I try to send a file directly using the default app it brings up Thunderbird even though Tbird is not showing in settings. I deleted Tbird and tried again but this time it tried sending through MS Outlook.
Rebooted PC but nothing changed. I was previously using Tbird as my default which worked as it should. Why cant I get emclient to be default?

Sounds like you may not have all the defaults set somewhere.

If you have Windows 10 or 11, see @Gary post there on the following thread below to see how to set all your defaults Including the MailTo: option. Reboot after setting all the defaults or it may not work.

Running Windows 11, ver 22H2. Had already changed Mailto to emclient from existing T bird

I’m sorry, but I am not giving Microsoft any more money. I am still using Windows 8.1 Pro. I have my defaults set in my OS properly. Is it Firefox that needs something set? Please advise.

You can ignore this request. Firefox DOES have a spot to change the mail program.