User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:56.0) Gecko/20100101 Firefox/56.0 Build ID: 20170926190823 Steps to reproduce: My Inbox folder has 11000+ messages in Maildir format. When I start folder repair of Inbox folder, memory usage of Thunderbird increases several GB and remains that high even after operation finishes. It is always reproducible. I'm using Thunderbird 52.4.0 (64bit) on Linux Gentoo. What to do: 1) Have an account in Maildir format 2) Have a folder with thousands of messages 3) Start folder repair (Folder Properties-> Repair Folder) 4) Watch Thunderbird memory usage (in my case it went from 135 MB to 7.9 GB) Actual results: Memory stays at 7.9 GB even after folder repair operation finishes. Expected results: It should have gone back to 135 MB.

Branimir, How long have you been using maildir? And how long has this problem been happening? Bug 1333342 reports something similar

(In reply to Wayne Mery (:wsmwk) from comment #1) > Branimir, > How long have you been using maildir? > And how long has this problem been happening? > > Bug 1333342 reports something similar I've just recently switched from KMail2/Akonadi to Thunderbird, so I can't tell if this problem existed in previous versions. The bug you referred looks like it's the same thing. Regards!

Let's combine forces then, in bug 1333342. If the fix to 1333342 doesn't help your situation we can reopen this bug