Problem with e-mail

My wife and I share the same computer, running Ubuntu Mate 20.04. We also share the same UM account. We use different browsers, Chrome for her, Firefox for me. I also use Thunderbird Mail.
We now have a problem which I was not able to solve: whenever she tries to send an e-mail from her professional site, clicking the "send message" opens an e-mail form from my Thunderbird.
How can I dissociate Google Chrome, the professional site and Thunderbird?
I have already uninstalled Thunderbird - after deleting my accounts - but that did not solve the problem.

In Firefox, Edit > Preferences, General, Applications.
Search for mail, it is set to open Thunderbird, I changed it to Always Ask.
Now, I click File > Email link ... FF pops a window what to do, I cancel.

HTH

Thank you very much. I checked my Firefox and it was indeed set to open with Thunderbird. Changed to "Always Ask", as suggested. I am not at home now, wiil try later to see how it now works.

Thanks again, most helpful.

Just to confirm that everything is working fine now.

Thanks again for your help.