Earlier we suggested improving the speed of Firefox by using a brand new profile. The trick is effective because it creates an almost virgin copy of Firefox sans any problematic add-ons or user settings that were probably causing Firefox to slow down.
James Meyer has written an alternate trick where you can make Firefox run faster even without losing any of the cookies, bookmarks or extensions.
He says: In my experience, what slows down Firefox is usually some preference for some installed add-on.
To fix the problem, make a copy of the pref.js file in your profile, and then edit it. The prefs.js file can be edited using notepad and it is available in your Firefox profile folder:
C:\Documents and Settings\[user]\Application Data\Mozilla\Firefox\Profiles\[xxx].default
Try removing lines that are related to various add-ons, and you will at some stage remove the line/lines that are causing the problem.
A method I have tried before is simply remove half of the lines, and try running Firefox with several tabs of pages with a lot of content. When you have identified the bad half, restore the original prefs.js file and remove half of that bad half and try again.
In this way, you can identify the lines that are causing the problem and won’t lose all your saved preferences.
Thank you James. As he suggested, make a backup of your Firefox Preferences file before deleting any lines.
Run Firefox 3 And Firefox 2 Together
Find this article at: http://www.labnol.org/software/browsers/speed-up-firefox-run-fast/2065/
Tags: Archives, firefox, Software, Web Browsers

Reader Comments
Yeah, thank you James! Good thing you’re not a surgeon or you’d have preferred a chainsaw to a scalpel.
Written by Frank Peligrino on 01.08.08
That all sounds a bit like too much trial and error for me. I haven’t got time to mess around deleting bits and pieces, testing to see if it’s faster or breaks, restoring the prefs backup and trying again deleting other lines.
There are some fundamental speedup settings you could try first. I wrote about them on Sig Figs last year – link – although those are more about load speed, I’m pretty much satisfied that FF runs as fast as it could on my laptop now.
Another alternative would be to run a raw copy of FF from your USB stick for times when you don’t need addons and simply want the fast surfing possible (use an online bookmarks manager to avoid having to synchronize favorites between hard disk and USB stick
db
Written by David Bradley on 01.09.08
Wow…thanks for the great information
Written by Narmadi on 01.09.08
hi amit,
i tried to reach the destination you mentioned above.i could not find the pref.js file.
instead after clicking on profiles, i found the folders related to bookmark backup,extensions etc.
pl can you clarify ?
Written by Sandeep on 01.09.08
I’ve been looking for this this files a few weeks ago to clean some uninstalled extensions in Firefox. Thanks for the tip! It will be very helpful!
Written by rodflash on 01.09.08
To Sandeep:
In Windows Explorer (Windows XP), try typing %HOME% to open your current profile folder. Your current “Application Data” will also be translated if you have Windows in another language.
Written by rodflash on 01.09.08
Hi
What the french word “sans” do in the first paragraph ?! :)
Written by Hicham on 01.09.08
Yeah, Firefox can really become a giant on clay legs and slows down to a crawl …
Nice tip
Written by Alex on 01.09.08
Thanks for the great tip… :)
Written by Niyaz PK on 01.09.08
i am using firefox 2. i tried it. first of all i was getting a new firefox window opened by running the command with -P option.
then i removed all the profile from the folder. and then run the same command again. then the manage profile doilog box appeared.
but not worthy. it looses all the settings. so i like to stick to my old profile with removing heavy add-ons.
Written by amit shah on 01.10.08
Personally I think Firefox is slow because of all the security settings that have been installed with each update, however I am willing to give the above advice a try.
I am hoping version 3 is better.
Regards.
Written by jsanderz on 01.10.08
hey thanx a lot mate. but i am havin some problem wid firefox. it gives an error everytime i try to install it. it says “cannot open file” also can u give some tip on optimizing opera browser???plz~~
Written by rambhai on 01.10.08
At last! It worked for me. Thank you. A nice quick fix, and easy to follow.
Written by johno on 01.12.08
Doing a binary search in the profile files !? LOL..
Anyway, nice tip. :-D
Written by Veerasundar on 01.13.08
Thanks for the excellent tip. Now I can restart a new profile with all my bookmarks intact while not being bogged down by the many Firefox add-on and extensions I have.
Written by Nascar on 01.13.08
What ever is done to speed up FireFox,it still hogs memory, that’s one of the biggest minus for it. Even Firefox 3 beta is behaving in that way, but little bit less of memory hog. Best way is to keep minimum number of addons installed for FireFox.
Written by vasudev on 01.14.08
why not simply use Opera browser.
recently i switched to Opera and believe me it’s ROCKING fast and stable.
it will open in a snap and some of basic things that i love to have in a browser (for which i’ll have to rely on Add-on in firefox) are in-built.
really it’s time to change to Opera.
FM.
goformails.blogspot.com
Written by FM on 01.15.08
This is a wonderful tip and it will be a useful one too.
Written by vhxn on 01.17.08
ATENTION!!!!
“Application Data” folder is HIDDEN. So go to Tools>Folder Options>View and select SHOW HIDDEN FILES AND FOLDERS and there you go. Now you can follow the path Agarwal wrote and you’l find your .js file.
Written by Waterproof on 01.23.09