ThunderFix

Thunderfix is a small tool that can fix Mozilla Thunderbird performance. If you have more GB of emails stored in Thunderbird and if you are experiencing slow start time, slow navigation through email folders, you might try Thunderfix. What Thunderfix does is that it detects *.msf files within your Thunderbird profile and removes them. After that, you can run Thunderbird and wait for new MSF files to be generated and you’ll see the improvement. With time MSF files become corrupted and can contain garbage, so this is quick solution for the problem. This way, the program runs smoothly and faster. If you want to read more about this issue and see how this tool works, check out this article. It supports version 2.0, but may work with older versions too. Use it at your own risk.

How to use it

    Close Mozilla Thunderbird.
    Choose your Thunderbird profile you with to fix (if you have only one profile, in most cases that is “default” profile).
    Thunderfix will count MSF files and will display the number below the profile name.
    Click “Fix profile” button.

http://www.parhelia-tools.com/products/thunderfix/thunderfix.aspx