This applies both to the current public version, 126.96.36.199, and the version currently up for review, 188.8.131.52.
I triggered this by the following:
1) Open http://enwp.org/Mahler
2) Click the status bar icon and select Edit Before Capture
3) Edit the page. I tried to use all of the functions from the edit toolbar.
4) Click save and complete the dialog that opens.
5) Close tab.
A compartment has leaked. I don't know how many of these steps are required to reproduce the bug.
Not CCing the authors as none seem to have Bugzilla accounts, but they have been notified via AMO.
.. correcting url.
Info request sent to the developer to ask them to cc onto this bug.
Developer chased via info request. If no response or updated version next week we'll downgrade existing versions to preliminary.
An update was uploaded with the intention to fix the bug, but it doesn't. I've notified the developer that the leak is still there and needs to be fixed soon.
Leak fixed in version 184.108.40.206 so closing bug.