With Windows 10 Build 10125 the whole titlebar becomes the accent color when the TB window is active. Correctly it should stay white with a small border with the accent color. Firefox is doing this correct (almost, it has a small bug with the border, bug 1167330). I correlated everything I could between TB and FX but found nothing different in CSS code. I added then a padding of 20px to the windows and saw a difference between TB and FX on inactive windows. TB's window is completely white and FX's window has a gray part in it (see attachment). I suppose FX initializes the window a bit differently than TB, but how and where?

Mike, do you have access to a Win 10 machine? If yes, please could you look with your deeper knowledge what TB is doing different to FX. If not, who could look at it?

Ha, looking more at the gray part of FX's content area made me remember that FX has a special -moz-appearance for win7's aero border shine which didn't worked for TB. But adding it now fixes this Win10 issue. :) I also removed a rule which is twice in mailWindow1-aero.css and primaryToolbar-aero.css.

I assume this is something that we can and should add in Thunderbird 38, probably at 38.1?

Comment on attachment 8609856 [details] [diff] [review] Bug1167929.patch [Approval Request Comment] Regression caused by (bug #): User impact if declined: Really weird appearance on Win 10 when TB main window is active Testing completed (on c-c, etc.): awaiting check-in Risk to taking this patch (and alternatives if risky): Low, only CSS change. If it can't land in 38.0 it should be in 38.1 to be ready when Win 10 is shipped.

Comment on attachment 8609856 [details] [diff] [review] Bug1167929.patch https://hg.mozilla.org/comm-central/rev/a47b6cb6dfcc

I've stared at Win10-TB-FX-comparison.png I I cannot figure out what the issue is. Can you try a little better to explain it? The only difference that I see is that the Firefox example has a gray vertical bar partway up on the left and right side of the active area. Is that what you are referring to?

(In reply to Kent James (:rkent) from comment #6) > I've stared at Win10-TB-FX-comparison.png I I cannot figure out what the > issue is. Can you try a little better to explain it? The only difference > that I see is that the Firefox example has a gray vertical bar partway up on > the left and right side of the active area. Is that what you are referring > to? This was an attempt to check the difference between FX and TB. Without patch (on image above) the active TB window looks like on Win 8 with a, in my case blue, titlebar. Win 10 has a white titlebar with a 1px blue border around the window, see on image below. The titlebar has actually a bug with showing a wider border on the left and right, but this is also on FX and a bug exists.

Comment on attachment 8609856 [details] [diff] [review] Bug1167929.patch http://hg.mozilla.org/releases/comm-aurora/rev/81353f66b394 http://hg.mozilla.org/releases/comm-beta/rev/f71314ee4d5d http://hg.mozilla.org/releases/comm-esr38/rev/720a4dbe6184