I'm gonna post this as a public service. 😉😊 Twice now, I've had a problem with Thunderbird opening links in the wrong browser -- each time occurred after a fresh installation of Kubuntu. A search seems to indicate this has been and is a problem for many users, Linux and Windows. There are posts on it here at KFN.
Twice, the following simple solution has worked for me:
Close your browsers and (especially) T-Bird. Under Kubuntu System Settings > Apps > Default apps, make your selection under default browser and click the Apply button at the bottom (if you don't do that, you will be prompted to do it). Test to see if T-Bird opens links in the browser of your choice. If not, close both the browser and (especially) T-Bird, go back to settings and make ANOTHER (different) choice for your default browser, and click Apply. Open T-Bird and see if the link you clicked opens in THAT new browser choice. Hopefully, it will. Now close browsers and T-Bird, go back to System Settings, and select your preferred choice for the default browser. Test again, and it should work OK, IME.
Sounds silly, maybe a little nuts, but twice this common sense solution has worked for me. The key seems to be in closing everything first, then making a (default browser) choice and clicking the Apply button to that choice.​
Twice, the following simple solution has worked for me:
Close your browsers and (especially) T-Bird. Under Kubuntu System Settings > Apps > Default apps, make your selection under default browser and click the Apply button at the bottom (if you don't do that, you will be prompted to do it). Test to see if T-Bird opens links in the browser of your choice. If not, close both the browser and (especially) T-Bird, go back to settings and make ANOTHER (different) choice for your default browser, and click Apply. Open T-Bird and see if the link you clicked opens in THAT new browser choice. Hopefully, it will. Now close browsers and T-Bird, go back to System Settings, and select your preferred choice for the default browser. Test again, and it should work OK, IME.
Sounds silly, maybe a little nuts, but twice this common sense solution has worked for me. The key seems to be in closing everything first, then making a (default browser) choice and clicking the Apply button to that choice.​