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FYI: Microsoft update for Windows 7 KB2670838 (date 2/28/2013) kills Firefox


Spent the entire morning troubleshooting this.

KB2670838 prevents FF from starting except in safe mode.

I downgraded from 19.0 to 18.0, same problem.

Went thru my entire system, reinstalled FF, nothing. The only difference in my system this AM was the MS update above. I removed it, rebooted and FF worked fine.

Modified by izaakb

Additional System Details

Installed Plug-ins

  • Shockwave Flash 11.6 r602
  • Adobe PDF Plug-In For Firefox and Netscape 10.1.6
  • Next Generation Java Plug-in 10.9.2 for Mozilla browsers
  • NPRuntime Script Plug-in Library for Java(TM) Deploy
  • SiteAdvisor
  • Adobe PDF Plug-In For Firefox and Netscape 10.1.4
  • 5.1.10411.0
  • The plug-in allows you to open and edit files using Microsoft Office applications
  • Office Authorization plug-in for NPAPI browsers


  • User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:19.0) Gecko/20100101 Firefox/19.0

More Information

Tyler Downer
  • Administrator
  • Moderator
1165 solutions 6639 answers

Helpful Reply

You can install that update and use Firefox if you Disable Hardware Acceleration in Firefox Turning off hardware acceleration