Quickly cleanup your Thunderbird IMAP folder cache
When you connect with multiple programs to your IMAP store, it is possible Thunderbird can be confused about what should be on the server and what it has on disk.
Result: Thunderbird just hangs with massive CPU usage.
A fix can be found at Mozillazine considering Phantom Folders.
A quick oneliner can solve the situation:
Quit Thunderbird, cd into your profile directory and:
find . \( -iname panacea.dat -or -iname *.msf -or -iname XUL.mfl \) -exec rm '{}' \; Open Thunderbird and everything should be fine again.