I just reformatted my computer (I try to do that about once a year) to Kubuntu 25.04. That meant setting up Thunderbird (version 128.10.0esr) with my email again. I use Firefox as my default browser (because it respects privacy), but install Chromium as a backup for the occasional website that doesn’t work very well with Firefox. Whenever I do that, for some reason, Thunderbird switches to opening links in Chromium rather than Firefox, which is annoying. On the face of it, it seems like it should open the links in Firefox because Firefox is set as my default browser in my system settings. Not sure what is happening. But here is how I solved the problem.
First, go to Edit -> Settings in Thunderbird.
On the General tab, scroll to the bottom and look for Config Editor:
Click on it. Then you’re going to search for two entries:
- network.protocol-handler.warn-external.http
- network.protocol-handler.warn-external.https
They will likely be set to “false.”
Click on the icon to the right to set them both to true.
Now, open an email in Thunderbird that has a link in it. Click on the link. It may or may not open in the correct browser. But we’re getting there. What this does is create a new option in your Thunderbird settings that you can modify.
Now, go back to Edit -> Settings. Again, on the General tab, scroll about halfway down the screen to where it says “Files & Attachments.” You should now see an entry for “https” (or http if the link went to an unencrypted website). You can now modify this option. I set mine to “Use System Handler (default)”.
Now, just to make sure, go into your settings in KDE and look for Default Applications.
Click on that and make sure that Firefox is set as your default browser.
Just an FYI, I had that set to Firefox, and it still wasn’t working. I then set Chromium as my default browser and hit Apply at the bottom. I then selected Firefox as my default browser and hit Apply again. Once I did that, everything worked. (It’s possible that Chromium tried to set itself as the default browser – sneaky bastards at Google – behind the scenes. Setting it as the default and then setting Firefox back as the default seemed to solve that problem.)
