Try running Firefox in Diagnose Firefox issues using Troubleshoot Mode. If it functions properly in that configuration, then one of your add-ons is the culprit.

See also: https://addons.mozilla.org/en-US/firefox/performance/

Safe Mode is no faster for me than with the few plug-ins I have enabled.

I actually don't have any add-ons, so that can't be the problem

I switched to Firefox from IE several months ago and found it to work much better. Now that I've upgraded for FF 4, it is worse than the previous version. I am unable to play games as they run much too slow. I was going to go back to the older version, but have read that it won't be supported for too much longer. I've gone back to using IE and it is much better. Playing games is 5X faster. I'll keep using FF4 for some apps. until it gets better.

Part of the problem may be due to the page you're visiting is drawing ads from other servers. You can avoid those by installing this add-on: https://addons.mozilla.org/en-US/firefox/addon/adblock-plus/

During the installation, you get the opportunity to subscribe to "Easylist". Confirm that and after Firefox restarts, go to https://adblockplus.org/en/subscriptions then go to the foot of that page and subscribe to Malware Domains. This is a security measure to prevent redirects to malware sites.

Also, install this add-on to prevent browser hijacks: https://addons.mozilla.org/en-US/firefox/addon/browserprotect/

i'm not great on comps or anything but i downloaded ff4 on my windows 7 and its great,better than chrome even since all that does lately,for months now on any comp i've used crashes nonstop,so thats when i went to moms she has a windows xp,i downloaded it hoping for same results,not only did it look different but it was super slow like others have said,i also have several others i know all with windows xp or older who had same issue..is this a compatibility problem maybe?sure seems like it...seems ff4 was made for newer comps..just a theory but its held up so far..i use safari as my backup now since chrome blew its gasket and no issues at all except facebook being slow sometimes but thats facebook for u..

@ bryanmm29, please perform a standard diagnostic. See Basic troubleshooting

For me, Safe Mode made a huge difference. Disabling the extensions one at a time, I found that the problem lay with the Ant Video Downloader (from ant.com). Once I disabled that, I was back up to normal speed with Firefox again.

In my case, it's got nothing to do with add-ons and plugins. Disabling them made no change in slowness or sluggishness in FF 4.0.1.

FIX: installed FF 3.6.18 (latest v3) over v4.0.1 with same add-ons and plugins. So so soooo much faster. Thank god, my sanity was restored.

PC: P4 3.4Ghz, 3GB RAM, countless HDD.

Switch to Google Chrome, much much faster!

Yah, i had the same problem and just disabled a few a add-on extensions and was able to open new tabs, websites and steam vidoes at a decent speed. You don't need to go into safemode to do this either....You might not even use some of the extensions you have enabled, so you should probably look into disabling some of the unnecessary ones.

This is not an issue with add ons!! Firefox 4.0 is awful. It's slow to load pages and I have to constantly reload pages to get them to display properly. Also, there are now so many incompatible items I used to use on firefox (Nectar toolbar is one example). This was never a problem before with the 'old style' Firefox. can I still download the old version anywhere?