How to completely remove Firefox from my iMac OS Big Sur 11.1

First when at your Desktop go to the Finder menu and select Preferences:

Next under General check all of the checkboxes that are there:

Now double click on the hard drive icon on your desktop titled Macintosh HD. You will see something like this:

Double click on the Applications folder to open it where you'll find then Firefox application.

+1

AppCleaner will do the job very nicely.

WARNING: If you use AppCleaner on an app that you have other apps from the same developer, like Adobe, you must be extremely careful checking all checkboxes and deleting.  Some for those other files may support other apps from the same developer and deleting them can mess them up.  Adobe apps is a primary example. I know from experience.  For singular apps from a developer it's safe.

the Application folder is where all of your apps (programs) are stored. It is located by first double clicking on your Hard Drive icon and then double clicking the Applications folder to open it. There you will find the icon for Firefox. Drag it into the trash and empty the trash. You will also find a Firefox icon alias at the bottom of your desktop in the Dock. Drag that icon into the trash as well and you're done.

Don't overlook these locations:

/Users/yourname/Library/Application Support/Firefox
/Users/yourname/Library/Application Support/Mozilla
/Users/yourname/Library/Application Support/CrashReporter/firefox*.plist
/Users/yourname/Library/Application Support/com.apple.sharedfilelist/com.apple.LSSharedFileList.ApplicationRecentDocuments/org.mozilla.updater.sfl
/Users/yourname/Library/Application Support/com.apple.sharedfilelist/com.apple.LSSharedFileList.ApplicationRecentDocuments/org.mozilla.firefox.sfl
/Users/yourname/Library/Application Support/com.apple.sharedfilelist/com.apple.LSSharedFileList.ApplicationRecentDocuments/org.mozilla.crashreporter.sfl
/Users/yourname/Library/Saved Application State/org.mozilla.firefox.savedState
/Users/yourname/Library/Preferences/org.mozilla.firefox.plist
/Users/yourname/Library/Preferences/org.mozilla.crashreporter.plist
/Users/yourname/Library/Caches/Firefrox
/Users/yourname/Library/Caches/Mozilla

All I can do is to repeat what I posted above. It is located in your Mac's Hard drive. Do you have a Macintosh Hard Drive icon on your desktop - upper right? If not, then do the following to display it. First, click on your desktop where nothing is displayed. Then under the Finder menu (next to the Apple logo) click Preferences. That will open a window that allows you to select the items to be showed on your desktop. Make sure that the first one is clicked to display the Hard Drive.

I would like ask a question! Why? If there is something wrong and you are just wanting reset things there is a way to do that which is a lot simpler then deleting Firefox. If you just want to remove it then the other suggestions that you received will work just fine. I am just curios that all.

You can go to the Applications folder and drag the app to the trash. Then empty the trash and done.

If you want to get rid of the app plus any hidden files use an app like Appcleaner. otherwise just drag Firefox app to the trash as noted.

I was wondering as well. I like Firefox. I have found it useful to have more than one browser installed because sometimes one or the other one will not work with certain web sites.