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Firefox slow on my MAC.


Firefox is suffering from seriously annoying lag spikes on my mac, while other browsers work perfect. The problem is the worst when watching Youtube video's or when typing (text only appears after 1-2 seconds when the spike happens.)

I've tried the about:config stuff, I used Speedyfox, googled for days but nothing seems to be working. What's worth trying? I love Firefox and I don't want to switch to another browser.

Could it be firefox plugin process? It seems to be eating a lot of RAM from times to times (I updated Java and Flash).

Thank you

Additional System Details

Installed Plug-ins

  • Version
  • Google Talk Plugin Video Accelerator version:
  • Displays Java applet content, or a placeholder if Java is not installed.
  • Shockwave Flash 11.5 r502
  • iPhoto6
  • Microsoft Office for Mac SharePoint Browser Plug-in
  • Facebook Video Calling by Skype
  • Simple plug-in that handles Citrix connection files


  • User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.7; rv:18.0) Gecko/20100101 Firefox/18.0

More Information

Everything is updated, Mac is running on snow leopard.
Almost no plugins and I tried disabling the once I have which didn't solve anything

Tyler Downer
  • Administrator
  • Moderator
1165 solutions 6641 answers

Helpful Reply

The Reset Firefox feature can fix many issues by restoring Firefox to its factory default state while saving your essential information. Note: This will cause you to lose any Extensions, Open websites, and some Preferences.

To Reset Firefox do the following:

  1. Go to Firefox > Help > Troubleshooting Information.
  2. Click the "Reset Firefox" button.
  3. Firefox will close and reset. After Firefox is done, it will show a window with the information that is imported. Click Finish.
  4. Firefox will open with all factory defaults applied.

Further information can be found in the Reset Firefox – easily fix most problems article.

Did this fix your problems? Please report back to us!

Question owner

Thank you for the reply, but will I lose my RSS feeds if I do this?

Tyler Downer
  • Administrator
  • Moderator
1165 solutions 6641 answers

Helpful Reply

No, you shouldn't lose them.

gslrider 1 solutions 22 answers

This was happening to me, and was driving me crazy! I came across an old thread (now closed). Tried it, and no more spike lags every couple of seconds. I set mine to 3600000, restarted Firefox, and no more lags.

From tklaus: At least for me, the problem was the session saver. Increasing the session save interval as described here eliminated the pauses:


  • Top 10 Contributor
  • Moderator
10762 solutions 96861 answers

Hi gslrider

How large is your sessionstore.js file?

You can check for problems with the sessionstore.js and sessionstore.bak files in the Firefox profile folder that store session data.

Delete the sessionstore.js file and possible sessionstore-##.js files with a number and sessionstore.bak in the Firefox profile folder.

Deleting sessionstore.js will cause App Tabs and Tab Groups and open and closed (undo) tabs to get lost and you will have to recreate them (make a note or bookmark them).

gslrider 1 solutions 22 answers

I was only able to locate sessionstore.bak (45k). No sessionstore.js in the profile folder. I'm currently running OS X 10.6.8.