Nightly builds as you know is a work in progress and due to the checkins and updates twice a day it can sometimes lead to issues until finished, fixed, or reverted.

It is possible the issue could be due to a change that was intentional or untended.

One place that some Nightly Testers hang out is in http://forums.mozillazine.org/viewforum.php?f=23 though a skim of listed bugs in last few days did not jump out as anything related.

If you create an account there the answer to captcha is 6 for the number of unique letters.

I posted here

http://forums.mozillazine.org/viewtopic.php?f=23&t=3046176&e=0

with no response

Continued here for Firefox 67, so locking this thread.

• /questions/1249086 mouse middle button click on ff nightly window top bar does not lower window on ubuntu