I strongly suspect this is windows only. To reproduce the issue: - Open testcase - Open the error console and make sure the top left of that window is layed over the testcase - Double-click in the left corner of that window to close it. Actual result: - Alert appears with 'mouseup fired' Expected result: - No alert should appear. This only happens with windows that are part of the same application. It reminds me a lot of bug 297080.

Not fixed by bug 297080. Matthew, do you know if this needs some similar tweaking of the code as you did in bug 297080?

I can reproduce this using Notepad over the top of the testcase too, so it's not just with windows that are part of the same application for me. What happens is the window disappears on the second mouse down (so mouse down + up + down -> close), so the final mouse up can end up being delivered to the lower window.

The same testcase using IE and Notepad does not cause the mouseup alert to appear. Is the problem that we're processing some events (e.g. mouseup) when we shouldn't be--that is, when the window is not focused? I'm not sure what the right/Windows way is here.

Ah, yes, I see that too now. Ok, I guess this is more a quirk than anything else. You might call this bug even invalid.

(In reply to comment #3) > Is the problem that we're processing some events (e.g. mouseup) when > we shouldn't be--that is, when the window is not focused? I'm not sure what > the right/Windows way is here. Well Im not sure if this is the same bug, but there is something similar in bug 184051 The problem there is that click event is fired every time when the mouse is used no matter which button, single or double click.

You can also get this mouseup problem if you double-click on a file in a file picker popup (i.e. <INPUT TYPE="file">), if the file is over the open window. The double-click only causes the mouseup if it closes the file picker too (double-clicking a folder works).