User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv:126.96.36.199) Gecko/20110303 Firefox/3.6.15 Build Identifier: Mozilla/5.0 (Windows NT 5.2; rv:2.0b10pre) Gecko/20110114 Thunderbird/3.3a2 In TB 3.1.x and earlier, all message headers "From, To, Cc, Subject" had colon (:) as the separator. For example "From:". But in TB 3.3a2, these colon (:) separator no longer exist, for example "from". This is not normal and need to be fixed. Reproducible: Always Expected Results: "From:" instead of "from"
I believe you have been using an add-on for your Thunderbird 3.1.x version - Thunderbird 3.1 has both the lower case letters and no colon. This is a duplicate of bug 478468 and a wontfix for the colon separator as I can't find a separate issue on that, though basically they are both covered by bug 478468.