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Firefox 19.0.1 "Class not registered" error on when you select menu item "Open Containing Folder" on a file in Downloads box.


On one of my clients PCs on a downloaded file in the downloads box if you right click and select "Open Containing Folder" and error box with a red x pops up with Firefox.exe in the title bar and says this"

Class not Registered.


Box goes away when you click OK. Unless you know the location of the file there is no way from Firefox to get there on this machine.

I have tried safe mode. I have tried a blank new profile. Same results.

Additional System Details

Installed Plug-ins

Unknown. This is not being posted on the machine with the issues.


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

More Information

  • Top 25 Contributor
617 solutions 4263 answers

Hello try to boot the computer in Windows Safe mode with network support (press F8 on the boot screen) and check it again.

otherwise, try a clean re-install, certain Firefox problems can be solved by performing a Clean reinstall. This means you remove Firefox program files and then reinstall Firefox. Please follow these steps:

Note: You might want to print these steps or view them in another browser.

  1. Download the latest Desktop version of Firefox from http://www.mozilla.org and save the setup file to your computer.
  2. After the download finishes, close all Firefox windows (click Exit from the Firefox or File menu).
  3. Delete the Firefox installation folder, which is located in one of these locations, by default:
    • Windows:
      • C:\Program Files\Mozilla Firefox
      • C:\Program Files (x86)\Mozilla Firefox
    • Mac: Delete Firefox from the Applications folder.
    • Linux: If you installed Firefox with the distro-based package manager, you should use the same way to uninstall it - see Install Firefox on Linux. If you downloaded and installed the binary package from the Firefox download page, simply remove the folder firefox in your home directory.
  4. Now, go ahead and reinstall Firefox:
    1. Double-click the downloaded installation file and go through the steps of the installation wizard.
    2. Once the wizard is finished, choose to directly open Firefox after clicking the Finish button.

Please report back to see if this helped you!

thank you