I hope you mean Thunderbird 34.

Auto correct is a function of the composer, it has plenty of bugs need fixing before anyone get to enhancements.

I suggest you contact the add-on author and see if there is an updated version in the pipe line you can have.

mms Auto Correct works here in TB 34 & 37. If you open Tools/Options/Advanced/General/Config. editor, copy autocorrect.wordsfile into the Search box and make sure it points to the correct location in your profile folder. This should be something like:

C:\Users\username\AppData\Roaming\Thunderbird\Profiles\mpftajqe.default\extensions\autocorrect@miller.micro\autocorrect.txt

Help/Troubleshooting Information, click Show Folder to open the profile folder.

http://forums.mozillazine.org/viewtopic.php?p=13672673#p13672673