I think thunderbird is a bit special, I'm not sure it respects the default settings for the browser. It's handled in its about:config dialog, check the value of "network.protocol-handler.app.http" key (cf. http://kb.mozillazine.org/Setting_Your_Default_Browser#Setting_the_browser_that_opens_in_Thunderbird_-_Linux for more info).
I think thunderbird is a bit special, I'm not sure it respects the default settings for the browser. It's handled in its about:config dialog, check the value of "network. protocol- handler. app.http" key (cf. http:// kb.mozillazine. org/Setting_ Your_Default_ Browser# Setting_ the_browser_ that_opens_ in_Thunderbird_ -_Linux for more info).