VERY helpful, although unstable with very large folders Rated 4 out of 5 stars

This was a lifesaver for me. I had a mailbox with 60,000 messages in it, about 10,000 of which were duplicates. This tool solved all my problems.

I ran it once on a mailbox without about 30,000 messages, and it worked flawlessly after I clicked through a "stopped script" dialog.

It ran less smoothly on the mailbox with 60K messages...it hung up and then crashed (exited) Thunderbird. But, I restarted the system and re-installed the extension and it worked...as long as I clicked through a bunch of "stopped script" dialogs and then ultimately clicked "stop", which dropped me into the review dialog. I then moved to trash, rather deleting outright, because deleting outright had also crashed Thunderbird.

All that said, I am so grateful for this tool. I didn't expect it to be able to process 60K messages at all, so the fact that I was able to get through it with just a few hiccups was a relief.

This review is for a previous version of the add-on (0.1.5). 

About that crash...

If you can e-mail me (or use savefile.com) an mbox file which triggers such a crash, or instructions on how to generate one, it would be most helpful. Although, in all fairness, it can't really be my fault, as JavaScript code (specifically, my code) should not be able to crash Thunderbird even if I tried - it's all sandboxed...