After upgrading from firefox-bin-35.0 to firefox-bin-36.0, any clickable link in emails opened with thunderbird results in opening a new browser window, but the URL is not passed and no page is loaded. I verified this by downgrading to firefox-bin-35.0. With this version everything works as expected. After upgrading the problem occurs. I use thunderbird-bin-31.5.0 on my system. Reproducible: Always
Okay, this is not a firefox issue, I'm sorry for the inconvenience. After changing the default Web Browser from "Mozilla Firefox" to "firefox" (firefox "%s") in Xfce, everything works as expected again.
User fixed the issue.
This happens with www-client/firefox-36.0 and mail-client/thunderbird-31.5.0, too. The workaround Marius Brehler mentioned works for me, too. Nevertheless since this happens only after the update to Firefox 36.0 and Thunderbird 31.5.0 without changing anything else I would still consider this a bug either in Firefox, in Thunderbird or Xfce except if it's a new feature. So maybe this bug report should be reopened. It's obviously only a minor issue.