Bad navigator launched

Hello, when I click on a link into the mail (on smartphone) , it tries to launch the system navigator (which is desinstalled) , and not my defaut navigator (firefox). I don’t find how to correct it.
Exception. When I click on k9/Menu/Parameters/Forum it launches firefox, the good navigator.
Thanks for your help.

I just tried and K9 opens the browser which is defined as Standard Browser. I changed it from Firefox to DuckDuckGo browser and it used it. If I removed the standard setting I will be asked what browser to be used.

Can you check in your Android settings what browser is set as Standard browser?

Android parameters is ok, fx my default navigator. When I click a link from other app like wechator whatsapp, all is working fine.
I repeat, when I click forum from the app k9, it works, but click from a mail launch the “OPPO” system navigator… which I’ve desinstalled.

Welcome to the forum, sadly, OPPO and other chinese devices tend to have these annoying default apps.
I assume this used to work previosuly tho. So I hope the devs find the cause of your problem