As per https://bugzilla.mozilla.org/show_bug.cgi?id=1471734#c8: As far as I can tell, hiddenWindow.xul is never referenced on non-mac (https://searchfox.org/mozilla-central/rev/ed2763bea882619ccb48b0aecc54e523d2bdd2ae/xpfe/appshell/nsAppShellService.cpp#126-129). This isn't about not using the hidden window in general (see Bug 71895 / https://searchfox.org/mozilla-central/rev/ed2763bea882619ccb48b0aecc54e523d2bdd2ae/browser/base/jar.mn#104), but just excluding the XUL hidden window from non-OSX builds, and then not preprocessing for OSX within the file itself: https://searchfox.org/mozilla-central/rev/ed2763bea882619ccb48b0aecc54e523d2bdd2ae/browser/base/content/hiddenWindow.xul#8.

Comment on attachment 8989266 [details] Bug 1472787 - Remove hiddenWindow.xul from non-mac builds Do you know of any cases where we actually do use hiddenWindow.xul in non-OSX? I can't see any, and no tests fail with the change.

Comment on attachment 8989266 [details] Bug 1472787 - Remove hiddenWindow.xul from non-mac builds https://reviewboard.mozilla.org/r/254318/#review261322

Pushed by bgrinstead@mozilla.com: https://hg.mozilla.org/integration/autoland/rev/260d05b38752 Remove hiddenWindow.xul from non-mac builds r=enndeakin+6102