My mum’s machine runs openSUSE 11.2, with KDE 4. She continues to use Thunderbird as her mail client as it is familiar. Naturally she also uses Firefox for web browsing.
Unfortunately, web links don’t seem to work which is rather annoying. Firefox is set as the default web client, as is thunderbird for email. My guess is that Thunderbird is looking for some GNOME configuration on what to do. I tried adding some custom handler arguements in Thunderbird’s config (like about:config in Firefox), but that didn’t work.
In the end, the simple fix was to use gconftool to set the appropriate parameters:
gconftool-2 -s /desktop/gnome/url-handlers/http/command
'/usr/bin/firefox %s' --type String
gconftool-2 -s /desktop/gnome/url-handlers/https/command
'/usr/bin/firefox %s' --type String
Restart Thunderbird and all is good!