I have Firefox and Thunderbird set as the default web browser and email client respectively, in KDE. Any link, whether it be in Konsole or Thunderbird, would open in Firefox as expected. The other day I installed Chromium which, on the first run, asks if you'd like to make it the default browser, and I declined. However, for some odd reason, Thunderbird now uses Chromium to open all urls. I checked to make sure that Firefox was still set as the default, and it is. Other applications, that would normally use Konqueror such as Konsole, still use Firefox. I tried to look for any Thunderbird setting that may have been changed using Edit -> Preferences -> Advanced -> Config Editor, but everything looks the same. I'm not sure what Chromium did, or perhaps KDE, that would cause this behavior.

I really don't want to muck with the config editor to get Thunderbird to use Firefox if possible, which I assume shouldn't be necessary given the circumstances.

maybe https://paolobernardi.wordpress.com/201 ... t-browser/

Well, I'm still not sure why Chromium was used as the default browser since I can't find any setting that uses it, but I believe the issue arose because when it was installed it altered ~/.local/share/applications/mimeapps.list in some manner. I was able to resolve the problem by resetting Firefox as the default browser through Firefox, rather than the KDE settings, which writes to this file. I don't think this is a KDE issue.

Thanks