Tap here to go to the mobile version of the site.
Your Firefox is out of date and may contain a security risk! Upgrade Firefox

Support Forum

Downloaded latest Firefox version but cannot open as say another version is already running even if I do not have it open. What is wrong?


Downloaded the latest version of Firefox on my Mac and it won't open as keeps saying that Firefox is already running. This keeps happening even after I log out and re-boot the computer. I don't understand why if I do a download to an existing operation it doesn't piggy-back onto the old one and function. Please help as I have looked at all your Q & A and did not find anything to address download won't work because older version still "running" even when closed. I have Mac OS X version 10.6.3. Thank you.

Additional System Details

This happened

Every time Firefox opened

This started when...

Tuesday, August 21, 2012 around 3:30 p.m. when I did first download.

Installed Plug-ins

  • Runs Java applets using the latest installed versions of Java. For more information: Java Embedding Plugin. Run version test: Java Information.
  • Gecko default plugin
  • Watch and download full length videos from your browser
  • npmnqmp 071505000006
  • http://www.facebook.com/fbplugin/
  • BrowserPlus -- Improve your browser! -- http://browserplus.yahoo.com/
  • DivX Web Player version
  • iPhoto6
  • Adobe Shockwave for Director Netscape plug-in, version 11.5.1
  • Coupons Inc., Coupon Printing FireFox Plugin
  • Displays Java applet content, or a placeholder if Java is not installed.
  • Shockwave Flash 10.3 r183
  • The QuickTime Plugin allows you to view a wide variety of multimedia content in web pages. For more information, visit the QuickTime Web site.


  • User Agent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.6; en-US; rv: Gecko/20100824 Firefox/3.6.9

More Information

Tyler Downer
  • Administrator
  • Moderator
1165 solutions 6640 answers

Try this:

  1. Open Firefox (or another Browser) up.
  2. Go to www.getfirefox.com
  3. Download the Firefox installer to your computer, and save it somewhere you will remember
  4. Restart your PC
  5. Install the new version of Firefox you downloaded (How to download and install Firefox on Mac)
  6. Restart your PC one more time, then Fire up Firefox

Hopefully it will work now and you should be all updated.

Modified by Tyler Downer

  • Top 10 Contributor
  • Moderator
10755 solutions 96800 answers

Create a new profile as a test to check if your current profile is causing the problems.

See "Basic Troubleshooting: Make a new profile":

There may be extensions and plugins installed by default in a new profile, so check that in "Tools > Add-ons > Extensions & Plugins" in case there are still problems.

If the new profile works then you can transfer some files from the old profile to that new profile, but be careful not to copy corrupted files.