I am running on Windows 7 x64, and whenever I try to use a version of Firefox newer than 17.0.1, I get the "couldn't load XPCOM" error, followed by two instances of
"FlashPlayerPlugin11_5_502_149.exe - Bad Image: C:\Windows\system32\msdmo.dll is either not designed to run on Windows or it contains an error. Try installing the program again using the original installation media or contact your system administrator or the software vendor for support."
Then Firefox closes. Every time I try to open it, this happens; it is unusable until I uninstall Firefox, delete the folder in Program Files, and reinstall 17.0.1.
The MSDMO.dll error shows up even in 17.0.1; I'm not sure whether they're related, but in 17.0.1 only one instance of it shows up shortly after I open FF, and then FF works normally.
The MSDMO error has been showing up since sometime last summer, but doesn't seem to interfere with much.
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.
Download the latest Desktop version of Firefox from http://www.mozilla.org and save the setup file to your computer.
After the download finishes, close all Firefox windows (click Exit from the Firefox or File menu).
Delete the Firefox installation folder, which is located in one of these locations, by default:
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.
Now, go ahead and reinstall Firefox:
Double-click the downloaded installation file and go through the steps of the installation wizard.
Once the wizard is finished, choose to directly open Firefox after clicking the Finish button.
I ran the System File Checker; it says msdmo.dll is corrupt and can't be fixed because the source file in store is also corrupt.
I think that I was actually wrong about the MSDMO and XPCOM errors being related; they're probably just showing up at the same time. The MSDMO error routinely shows up when I load the website imo.im, and I usually have a pinned tab of that site. So although the msdmo error is irritating and confusing, it is probably not actually tied to the xpcom error.
I'm still tooling around with the clean install, but so far it isn't working at all. I've also tried installing in an entirely different folder; no luck there, either.