Did you try to reinstall? https://www.firefox.com/en-US/?redirect_source=mozilla-org

I attempted to reinstall 4 times. Each time I got the message, "Firefox already installed, let's update", then near the end of the update, I got the, "unable to load XPCOM", message. Before I tried to reinstall, Firefox would not open and I got a message saying something like, "Unable to load exe program".

Thankyou for your response.

WOW. Did you delete all these files. see links https://support.mozilla.org/en-US/questions/1229392 https://support.mozilla.org/en-US/questions/1100145

Get Firefox from Mozilla. https://www.firefox.com/en-US/download/all/?redirect_source=mozilla-org

Also try a different version of Firefox(Beta, Dev, or Nightly) and see if you have the same issue. Make sure to install in a different directory than your current install. https://www.mozilla.org/en-US/firefox/channel/desktop/

AI Overview: The "Cannot load XPCOM on update" error in Firefox (or Thunderbird) means a failed update left mixed files, often due to security software blocking changes, a corrupted profile, or a virus; the fix usually involves a clean reinstallation by downloading a fresh installer, temporarily disabling antivirus, and manually deleting old program folders (like C:\Program Files\Mozilla Firefox) before running the installer, which preserves your profile data.

What security software besides MS Defender are you running?

I'm not running any security programs other than MS Defender. As I'm sure you surmised, I did not uninstall Firefox before trying to reinstall. I just finished reading the threads you posted above and was going to try that next. I should mention that the laptop this problem occurred on is not often used for anything other than music storage and playing through bluetooth speakers. I primarily use my phone for most online purposes, but was reserving flights for a visit to family and tired of the small screen and mobile site, so I tethered this laptop to the phone to continue my search. I also have a chromebook laptop dedicated to my auto hobby–repair manual storage and restoration info, and when I was unable to fire up the PC tried that one, but was unable to open Firefox there, either–no error messages though. Obviously, since they are almost never used online, they are seldom updated.

Thanks again for the response, and I'll try a clean install and report my results