Build and register ISimpleDOM proxy ourselves (AKA fix broken math in Firefox/Chrome on some systems)

[jcsteh]

Steps to reproduce:

1. Open this URL in Firefox or Chrome: data:text/html,<math><mi>x</mi></math>
2. Use the cursor keys to read the document.

Expected behavior:

"x" should be reported.

Actual behavior:

On some systems/builds of software, nothing is reported and the following is logged:

DEBUGWARNING - NVDAObjects.IAccessible.ia2Web.Math._get_mathMl (11:45:38.736):
Error retrieving math. Not supported in this browser or ISimpleDOM COM proxy not registered.
Traceback (most recent call last):
  File "NVDAObjects\IAccessible\ia2Web.pyc", line 63, in _get_mathMl
  File "comtypes\__init__.pyc", line 1078, in QueryInterface
COMError: (-2147467262, 'No such interface supported', (None, None, None, 0, None))

Additional info:

This occurs when the 32 bit and/or 64 bit ISimpleDOM COM proxy is not registered. (For 64 bit browsers, we need both.) This can happen for several reasons:

1. 64 bit builds of Firefox don't install the 32 bit proxy. This will only become more prevalent as more users migrate to 64 bit builds.
2. I suspect (but am not certain) that Chrome doesn't ever install the proxy, regardless of bitness.
3. If you uninstall a Mozilla app while other Mozilla apps are still installed, that might unregister the proxy.
4. Possibly other obscure edge cases I haven't thought of.

The key point is that we simply cannot rely on this being installed correctly. Instead, we should build it and register it ourselves using CoRegisterClassObject/CoRegisterPSClsid as we do for IAccessible2 (see installIA2Support in nvdaHelper/remote/IA2Support.cpp).

P2 because this breaks math support for Firefox and Chrome for an increasing number of users.

[NSoiffer]

Would a 64-bit build of MathPlayer be a better solution for you? Or is this a problem you need to solve for other reasons also?

[jcsteh]

No; NVDA is 32 bit (and we have no plans to change this at this point), so we use 32 bit MathPlayer. Also, this relates to the way we access MathML in Firefox/Chrome, rather than how we process it after that. Thanks for your interest, though!

[NSoiffer]

I'm not 100% clear on whether this means that NVDA works with MathML in 64-bit FireFox and 64-bit Chrome. It sounds like the problems with the proxies was fixed, but I didn't see anything in the comments saying that math was tested with 64 bit versions of the browsers. Is it fixed, or should I open a new issue?

[michaelDCurran]

This will certainly work with 64-bit.