As of today, 2014-01-07, I am running Firefox 26.0 on Windows 8 with the Adobe Flash Plugin 11,9,900,170.

For the past few weeks, whenever I attempted to load a site that utilizes the flash plugin, I would receive an application crash error with the following details:

Problem signature:

  Problem Event Name:                        APPCRASH

  Application Name:                             FlashPlayerPlugin_11_9_900_170.exe

  Application Version:                           11.9.900.170

  Application Timestamp:                    529b79bf

  Fault Module Name:                          StackHash_fa66

  Fault Module Version:                        0.0.0.0

  Fault Module Timestamp:                 00000000

  Exception Code:                                  c00001a5

  Exception Offset:                                PCH_1C_FROM_ntdll+0x0002DC34

  OS Version:                                          6.2.9200.2.0.0.256.48

  Locale ID:                                             1033

  Additional Information 1:                  fa66

  Additional Information 2:                  fa6696398de2b9f98383d7a3bf5c3ea1

  Additional Information 3:                  fa66

  Additional Information 4:                  fa6696398de2b9f98383d7a3bf5c3ea1

 

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And I found tips all over the ‘Net for how to resolve it, but most of them advised to reinstall the Flash plugin, which I had done many times to no avail, or to perform an application repair from the Control Panel, which was also not helpful in my case. I finally found the answer, via a mention of mms.cfg in this Mozilla support forum post: https://support.mozilla.org/en-US/questions/969522?esab=a&s=uac&r=3&as=s, and then the details via this forum page from Adobe: http://forums.adobe.com/thread/1018071?tstart=0

The fix for me was to simply disable Adobe Flash’s Protected Mode via editing C:\Windows\SYSWOW64\Macromed\Flash\mms.cfg and adding the line:
ProtectedMode=0
then saving & closing the file, restarting Firefox, and reloading the Flash plugin (via visiting a site that uses Flash and activating the plugin.)

I don’t believe this to be the “Correct” fix, and this will need to be revisited in the near future, but there is definitely some type of incompatibility with Firefox 26.0, Windows 8, and Flash 11.9 (and according to the first forum post I linked up, Flash 11.8, as well. Users of other operating systems appear to have this problem at times, too, including Windows Vista, Mac OS X (not sure which version), and at least one Linux user (not sure which distro, version, or any other details.) — This informs me (anecdotally) that this may be inherent in some part of the Flash libraries, not the host OS.)

Regardless, that is how I solved it, and it took my considerable time to find the correct fix for me, so I am posting this here to help with Google searches for either the StackHash error code “StackHash_fa66” or “fa6696398de2b9f98383d7a3bf5c3ea1” or for searches on the DLL error code “PCH_1C_FROM_ntdll+0x0002DC34”

Best of luck to you!