As the latest spec shows, the buttons that are along the right side of the preferences should have a min-width of about 150px. Some buttons, such as the "Change master password...", button will have to be wider but all buttons can have a min-width of 150px. This will help the preferences look more aligned. See spec: https://mozilla.invisionapp.com/share/P4ACQT1E3#/screens/217167680

I measured the spec again and it's closer to 145px so I went with that.

Comment on attachment 8858390 [details] Bug 1356508 - Buttons on the right-side of the preferences UI should be mainly uniform in width. https://reviewboard.mozilla.org/r/130332/#review133934 Sorry for the delay, thanks! Note that I didn't test this patch manually.

Pushed by jwein@mozilla.com: https://hg.mozilla.org/integration/autoland/rev/369e9c270e27 Buttons on the right-side of the preferences UI should be mainly uniform in width. r=mconley

Screenshots of the change: https://screenshots.mattn.ca/compare/?oldProject=mozilla-central&oldRev=3f9f6d6086b2d247831d1d03d530095bebd5a6b2&newProject=mozilla-central&newRev=2458112439037abae9e72fc0612b75fe7a82344d&filter=_preferences_

I have reproduced this bug with Firefox nightly 55.0a1 (2017-04-14) on Windows 10, 64 Bit. The Bug's fix is now verified on latest nightly 55.0a1 . Build ID 20170502030211 User Agent Mozilla/5.0 (Windows NT 10.0; WOW64; rv:55.0) Gecko/20100101 Firefox/55.0 [bugday-20170502]