This site will have limited functionality while we undergo maintenance to improve your experience. If an article doesn't solve your issue and you want to ask a question, we have our support community waiting to help you at @FirefoxSupport on Twitter and/r/firefox on Reddit.

Search Support

Avoid support scams. We will never ask you to call or text a phone number or share personal information. Please report suspicious activity using the “Report Abuse” option.

Learn More

Firefox slow on my MAC.

  • 6 replies
  • 20 have this problem
  • 10 views
  • Last reply by gslrider

more options

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

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

All Replies (6)

more options

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 Refresh Firefox - reset add-ons and settings article.

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

more options

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

more options

No, you shouldn't lose them.

more options

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:

http://www.techmynd.com/firefox-freezes-for-a-moment-after-every-10-sec-fix/

more options

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).

more options

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.