I upgraded to 43.0.1 of Firefox and now Thunderbird 8.0 does send emails anymore (incoming email is ok). I keep getting a Comcast error "Too many sessions opened". I drove Comcast crazy trying to pin the blame on their smtp server, but then i tried with my two laptops that use the same smtp server and outgoing email works just fine on both (both have old Firefox and old Thunderbird). Then i realized that the problem started happening exactly after i installed the new release of Firefox. Even weirder: i switched to another (non-Comcast) smtp server and i still get the error message as if i am using the Comcast smtp server. The screenshot is exactly the same whichever smtp server i use. <i>(Thread closed. Duplicates are not permitted. [https://support.mozilla.org/en-US/kb/forum-rules-and-guidelines#w_posting-support-requests See forum rules and guidelines] ~m)</i>