Trash Firefox 4, and then install Firefox 3.6. You can get the latest version of Firefox 3.6 from http://www.mozilla.com/en-US/firefox/all-older.html

This is the first time that I have had a problem with a Firefox update. Does this mean that my computer is no longer secure to use Firefox? Do you think that I will be able to update to a version 4.+.+ when it is developed in the future?

firefox 4 is only slow with windows 7, as i have installed firefox on a computer with windows vista and it works great!

Bonjour Tony, thanks for the input on restoring 3.6, but my understanding is that there are files that need to be saved from 4.0 to place back in 3.6 AND certain files that need to be deleted from 4.0 so they will not corrupt 3.6. I saw this on here and cannot find it again. I know it sounds confusing but I don't want to lose anything. So I want to be absolutely positive before I take this step into the unknown. Merci beaucoup!

Thank you but a box popped up and told me something was wrong with me download. I reinstalled and now it's good again. Took 2 days to tell me but better late than never.

@mjmcfarl3; Firefox is not only slow on windows7, I installed it in Ubuntu Linux and its terribly slow! Within 5 minutes surfing I closed Firefox and installed an other browser, WOW what a difference! I try FF two times again with the same result and for the first time in 5 years I quit FF.

Ya, unfortunately FF 4.0 on Ubuntu has been incredibly slow, and is locking up my system. I have in many years of running server and Desktop client versions of Linux, presently Ubuntu, never had lockups like this.

A bummer, because have been a faithful FF user. Can't now. Lock ups really surprise the bejeepers out of me.

Firefox 4 is not only slow on Windows 7 & Ubuntu but also on Windows Vista.

Long start up times, long waits for locations to open, RAM wrapped up to the max, navigation toolbar buttons randomly getting larger (larger than you can choose in options).

I can appreciate that many of the add-ons will need to be updated in the interim, but one,- FEBE, is sorely missed, certainly in the face of this problematic upgrade.

I also will be downgrading to 3.6 for now

Same problem in OS X 10.5. Firefox requires a full second or two to become responsive again between clicks. This includes link clicks, closing a tab, accessing menu, etc. Still, my first suspicion would be that one of my plugins could be the culprit. If after investigation I'm able to uncover anything, I will post back here.

I decide to go through and thin out my add-ons anyway, but it definitely was an add-on that was causing the slow-down. Now it's blazing again.

Add-ons I disabled (ie, one of these or combination of, is the bad guy):

• Measure It
• Rainbow
• Tag in Text Area
• Define

Still Good Guys:

• StumbleUpon
• Firebug
• Ad-Block
• Greasemonkey
• XMarks

Mine appeared to be LittleFox ... once I removed the extension and restarted FF4 ... back to normal blazing speed that I love! Good guidance on this one.

I have windows vista and it is extremely slow on here. I am tired of the way it pauses when I am typing or the fact that it takes forever to load up a page. I might as well have stayed on dialup instead of getting high speed. If Mozilla isn't going to fix it or respond to the thousands of people who are complaining about this new update, I am moving my bookmarks, everything over to chrome until firefox is fixed.

I had a slow rendering problem with Firefox 4. It was a brand new system : Fedora 15 + Firefox 4 on Intel motherboard with Ethernet controller: Intel Corporation 82579V Gigabit Network Connection (rev 05). It was very puzzling because Firefox was slow but when downloading a huge file, I was downloading at full speed. I turned off the IPV6 (as discussed here http://kb.mozillazine.org/index.php?title=Network.dns.disableIPv6&printable=yes). It helped but that didn't solve everything. After hours of searching, I found that it was not a problem with Firefox but a problem my ethernet controler driver. When doing the command ping in a terminal window, I found I was loosing a lot of packets. I found the driver (named e1000e) provided with the Fedora live disk is not working properly. You have to build your own driver. I had to go to http://downloadcenter.intel.com/, find the right package for my ethernet controler 82579V and follow the instruction in the README file.

I've done that successfully and now Firefox works full speed !