Firefox/Gecko control interfering with Windows Forms key presses

Question

Edit: In addition to the bounty, we're willing to pay $250 to have this bug fixed in the Firefox/Gecko codebase. Here is a simple test project (Visual Studio 2008 C#) that reproduces the problem.

Edit #2 we're willing to pay $600 to have this bug fixed. See above for sample project that reproduces the problem.

We have a Firefox (Gecko) ActiveX control on our C# Windows Form to display HTML.

When this Firefox ActiveX control is on our form, about 2-3% of our key presses don't make it through. Or rather, a different Windows message is sent:

We hold down the TAB key to tab through 3 regular WinForms text boxes. It will behave correctly 97% of the time. Spy++ tells us WM_KEYDOWN message is sent properly:

normal behavior http://judahhimango.com/images/normaltab.jpg

But randomly, maybe 2-3% of the time, the tab key (or other key) isn't processed right. Spy++ tells us WM_CHAR is being sent instead:

odd behavior http://judahhimango.com/images/screwytab.png

When the odd behavior occurs, either the key is not processed at all, or is processed incorrectly (such as inserting a '\t' character into a textbox that doesn't support tab characters.

This only occurs if the Firefox ActiveX control is on our form.

Our question is: does Firefox/Gecko engine install some kind of keyboard hook that might cause these side effects? Or better yet, how do we fix this problem?

Answer 1

The WM_CHAR message is generated by TranslateMessage call, so a good place to start looking would be the TranslateMessage calls in the Gecko source code.

In the first example code you provided the function is imported only by two libraries - mozctl.dll and xul.dll. Since you claim that the same error happens also with GeckoFX we can take mozctl.dll out of the equation. That leaves us with xul.dll, so given the Gecko source code I would suggest to look into widget\src\windows\nsToolkit.cpp. I am not sure if the code is run if the engine is embedded, but if it is then the library starts a whole new message pump in different thread, which is bound to break.

Unfortunately I can't run or compile the code on my machine (Windows 7 x64 w/o the Mozilla ActiveX control installed), so I can't verify any of this with a debugger. Hope it helps someone to track it down further.

Answer 2

The root problem is that when Mozilla is embedded in another application, it incorrectly pumps Windows messages when it dispatches internal events. Mozilla uses an event system to coordinate across threads or to schedule deferred processing on a thread (see nsIThread, nsIEventTarget). If you embed a web page with a lot of active XMLHTTPRequests, for example, Mozilla will use its event dispatching interface to dispatch events back to javascript and it will pump windows messages as a side effect. Once Mozilla events are fully dispatched, it goes back to the main event loop.

When Mozilla pumps windows messages, it doesn't include the extra processing done by the application's event loop - IsDialogMessage(), TranslateMessage(), PreTranslateMessage(), or any other pre-processing are skipped when Mozilla gets into this state. Symptoms therefore include tab key presses getting inserted as a character instead of being used for dialog navigation, keyboard hotkeys being sporadically ignored, or custom message pre-processing being sporadically skipped. For example, the Outlook 2007/2010 "Compose" screen sporadically loses keystrokes because it relies on custom message pre-processing to handle keyboard input.

See https://bugzilla.mozilla.org/show_bug.cgi?id=582790 for a patch that addresses the problem.

Answer 3

I have Snoop Free and PSM Anti-Keylogger. One of them detected firefox trying to install a Keyboard Hook. Mozilla/Firefox file xul.dll attempt at installing at keyboard hook. DENIED.

Answer 4

I noticed that you have implemented all of the interoperability yourself. Can you try this with the GeckoFX project and see if you get the same error? I use this project at work and haven't encountered any issues yet.