Here's what you have to do to fix the missing Titlebar in Thunderbird when using certain Windows 7 Styles with 1px border like my Maverick for Win7 or Minimal Taste Reloaded.
1. Go to your Thunderbird installation folder and backup the file omni.jar. For those using Thunderbird Portable you can find the file at: ThunderbirdPortable\App\Thunderbird\
2. Unpack the content of this archive
3. Copy the file omni.jar from the archive to the root of your Thunderbird installation folder, or for those using Thunderbird Portable copy the file to: ThunderbirdPortable\App\Thunderbird\
4. Start you Thunderbird email client and email away without having to worry about the Titlebar ever disappearing again!Also don't forget to check out the Firefox Fix as well: [link]