Seems like the easiest way to make Thunderbird properly work on PCLOS using KDE is to do this:
- Go to the config editor (Edit->Preferences==>Advanced->General->Config Editor)
- Agree to the warning if it pops up
- Enter this into the filte box at the top: network.protocol-handler.warn-external.http
- Double-click each entry shown to change it to true.
- Close the Config Editor.
- Click a http or https link, and wait for the dialog box to open asking what application to use.
- Click on Choose and browse to a web browser ("/usr/bin/chromium-browser" for example)
- Place a check where it says to "Remember my choice" if desired.
- Profit!
This also works if you click an internal T-bird link, such as "Get Themes" in the Add-ons dialog box. There is a noticable delay before that box pops up tho in that case. Just wait a minute and all will be fine.
More details here at the PCLOS forums.