STR : - Create a new window (either launch Firefox, or click "New Window") - You get what's in the screenshot intermittently (not often though)

See https://bugzilla.mozilla.org/show_bug.cgi?id=1173725#c124 for more details.

Jim, can you investigate what's going on here ? (I'm fairly sure it's related to bug 1187153 too). Those 2 bugs used to happen on Windows 8 and Windows 7 as well when custom caption buttons were used. May as well be related to the chromemargin.

Do you see this without e10s?

(In reply to Jim Mathies [:jimm] from comment #3) > Do you see this without e10s? I haven't checked on Win 10, but the same issue occured on Win 8 and 7 (e10s enabled or not) when custom caption buttons were used (via an userstyle)

Hmm, I can't reproduce on Win7 using the following str: 1) set your home page to google.com and specify it should be loaded for new windows through options 2) using ctrl-t, open twenty windows result: window content bounds looked fine in all new windows.

(In reply to Jim Mathies [:jimm] from comment #5) > Hmm, I can't reproduce on Win7 using the following str: > > 1) set your home page to google.com and specify it should be loaded for new > windows through options > 2) using ctrl-t, open twenty windows > > result: window content bounds looked fine in all new windows. You need custom caption buttons. Try this userstyle : https://userstyles.org/styles/104729/devfox (Enable the custom window frame option). You may also need to reduce the chromemargin.

P4 based on this not being a default config nor a regression in Windows 10, but it bothers me a bit more than a normal P4 because the cause-and-effect is not at all going to be obvious to a user who has done this.

(In reply to Justin Dolske [:Dolske] from comment #7) > P4 based on this not being a default config This is now the default config on Windows 10, we use the custom caption buttons, which causes this bug. This is on 100% DPI too. Although, since this is hard to reproduce I agree about the priority.