1192515 - KeyboardEvent misfiring issue with the AltGr key

Status: RESOLVED INVALID

(Firefox :: General, defect)

Description

[phi2x]

Attachment: Firefox KeyboardEvent misfiring issue for the AltGr key.png

I've tested Keyboard Events in Firefox 39 on Windows 10 with my French keyboard, and see how it behaved for each key.

What I found is that Firefox doesn't handle correctly the AltGr key.
When I press the AltGr key it fires the 'AltRight' key event as it should.
But it also fires the 'ControlLeft' key event at the same time.
As I never pressed the 'ControlLeft' key, it's clearly a bug of Firefox.

I attached a screenshot showing what I get using the W3C Keyboard Event test when I press the AltGr key.

Comment 1

[phi2x]

I investigated a bit more.
The behaviour is actually the same in the other browsers I tested: Chrome and Edge.
So this bug is not Firefox specific. Weird.

But still, I think that the AltGr key should not trigger the 'ControlLeft' key event.

Comment 2

[phi2x]

Ok, I found the root cause. It's a bug of Microsoft Windows (all versions).

Here's what I found on the cygwin mailing list:
http://cygwin.com/ml/cygwin-xfree/2011-08/msg00000.html

"The actual issue here is that Windows apparently inserts a fake Ctrl-L keypress/release when AltGr is pressed/released (except when the keyboard layout is US).
I have never found any documentation of this behavior, and I've no idea why it does this."