Thunderfix is a 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. 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.