You can try these suggestions:

• delete the Firefox icon from the dock
• create a new icon by dragging the Firefox application to the dock
• reinstall Firefox

Current Firefox release:

• https://www.mozilla.org/en-US/firefox/all/

Cor-el,

Thanks for your advice. I was able to reinstall Firefox. I did not lose my stored logins and passwords. Thank you!

How do I remove it from dock? Also, in applications, the incorrect icon is there also

What seems to help in most cases I've seen is dragging the current Firefox application in the Finder to the trash and reinstall Firefox.

Download a new copy of the Firefox application and save the Disk Image file to the desktop Firefox 64.0:

• https://www.mozilla.org/en-US/firefox/all/

• trash the currently installed Firefox application (open the Applications folder in the Finder and drag the Firefox application to the Trash) to do a clean reinstall
• install the new version that you have downloaded
• https://support.mozilla.org/en-US/kb/Installing+Firefox+on+Mac

Your personal data like bookmarks is stored in the Firefox profile folder, so you won't lose personal data when you reinstall or update Firefox, but make sure NOT to remove personal data when you uninstall Firefox as that will remove all Firefox profile folders and you lose your personal data.