How to Fix ‘A Copy of Firefox is Already Open’ Error on Mac

Seeing the “A Copy of Firefox is Already Open” message when trying to open Firefox on your Mac? This frustrating error prevents Firefox from launching even after force quitting or restarting.

Luckily, there are several effective methods you can use to troubleshoot and fix the “A Copy of Firefox is Already Open” problem on Mac.

Now, I’ll outline the top solutions to try when faced with this Firefox error, including:

• Using Terminal to delete duplicate profiles
• Removing Firefox lock files
• Force quitting all Firefox processes
• Ending Firefox tasks via Activity Monitor
• Reinstalling or updating Firefox

Read on for step-by-step instructions to get Firefox running again on your Mac.

Why the “A Copy of Firefox is Already Open” Error Occurs on Mac

Before jumping into the fixes, let’s briefly look at why you might get the “A Copy of Firefox is Already Open” message.

This error typically appears due to:

• Multiple Firefox profiles causing conflicts
• Corrupted Firefox lock files
• Firefox processes running in the background
• Issues with Firefox installations or updates

Ways to Resolve ‘A Copy of Firefox is Already Open’ Error on Mac

Luckily, the solutions below address the various causes of this error to relaunch Firefox.

Fix #1: Use Terminal to Remove Duplicate Profiles

One common trigger for the “A Copy Already Open” error is having multiple Firefox profiles. You can use Terminal to identify and remove duplicate profiles:

1. Open Terminal
2. Type /Applications/Firefox.app/Contents/MacOS/firefox-bin -P and hit enter
3. Look for more than one Firefox profile and delete any duplicates
4. Restart Firefox to see if the error is fixed

This eliminates profile conflicts that can prevent Firefox from opening.

Fix #2: Delete Firefox .parentlock Files

Corrupted Firefox lock files can also cause the “A Copy Already Open” message. To remove troublesome .parentlock files:

1. Open Terminal
2. Enter rm -f ~/Library/Application\ Support/Firefox/.parentlock
3. If that doesn’t work, delete the entire Firefox support folder
4. Launch Firefox again to see if the error has cleared

Deleting old Firefox lock files often resolves the issue.

Fix #3: Force Quit All Firefox Processes

Firefox processes running in the background can sometimes trigger the error. Thoroughly force quit all Firefox processes:

1. Right-click the Firefox icon and select Force Quit
2. If that option isn’t there, press Option + Cmd + Esc to force quit
3. In Terminal, enter killall -9 firefox to end all processes
4. Try opening Firefox again after force quitting

This stops any hidden Firefox processes that could be causing the conflict.

Fix #4: End Firefox Task via Activity Monitor

You can also use Activity Monitor to isolate and force quit the Firefox task:

1. Open Activity Monitor in Utilities
2. Click the Processes tab
3. Find firefox and right-click to select End Task
4. After closing out the process, relaunch Firefox

Activity Monitor provides another way to force quit the Firefox process preventing startup.

Fix #5: Reinstall or Update Firefox

If the above fixes don’t resolve the issue, try reinstalling or updating Firefox:

• Fully uninstall then reinstall the latest Firefox version
• Or open Firefox and check for updates to upgrade
• Restart after reinstalling or updating

Hope this helps!