Works fine for me.

it's slow for me only on youtube , takes a few refreshes for videos to load correctly , I wish chrome fixed the surround sound issues already :S

According to the changelog, they made a new JavaScript engine. Which claims to be about 25% faster.
I did some online tests, and the results were much better, and the browser really feels faster to me.

Try different browsers (Opera, IE) to check if it's just your connection.

No problem

I cleaned out my computer to see if that was the reason. It is chugging pretty bad.

Firefox has been getting worse for years. I switched to Chrome a year ago and I will never go back.

Works fine over here.
It could be a faulty add-on or extension that hasn't been updated.
Try disabling your add-ons or start firefox with add-ons disabled.

Or try making a new Firefox profile and see if that works.

Did you try uninstalling and reinstalling?

I stopped using FF when it launched updates 5,6,7 etc in 1 week. Now I'm using Chrome and it's just so much better and it has a better design. Anyways, it was acting buggy when I last used it, so yeah..

No problems from me. I have both Chrome and FF.

Chrome is a lot better than firefox, atleast for me! :D

It has gotten a lot worse for me with the latest update. Even crashes if enough tabs are open at once. I will be trying Chrome again in the next day or 2.

Just you. Mine is okay

Both my main browser SRWare Iron & Waterfox are running normally forever but I'm a new user in here, so for the past weeks :D.
Is there any chance you are using something like a broken script which could slow it down and provoke that ? (I assume we are all using the armada of addons addblock/ghostery/KB enforcer/fasterfox/etc like and since you mentioned you disabled them Its probably not due to that but worth the try...).
Sounds like you are going to reinstall FF if that doesn't go better, before you do, you might give it a go to Pale Moon or Waterfox (FF optimized builds and I only use the last one so can't really compare), bit faster and still using the FF full profile (so no loss) before anything else.
I have to say that Waterfox last version is still 16.01 and that's the closest I can relate to, don't blame me for trying to help please :P

same here... for about 1 or 2 years there was some updates in a short time... sicne there my firefox is hanging and lagging... and sometimes it stop working correctly. and i know its not in the first case firefox. the main reason why firefox stop working is adobe flashplayer.. if i kick the flash player with the task manager i just must reload the webpage and everything is fine

I never get the updates right away, sitting at two versions behind usually.

Firefox is a "heavy" browser that gets heavier after each update.
The issue probably is:
1) your computer isn't good enough for it (solution: upgrade hardware)
2) your ram is full (solution: fromat/ uninstall some random crap you don't need}

Still the same for me. But Opera is my primary browser though.

I use FF for some websites Opera can't load well.

I would presume it has something to do with your OS, Windows 8. I recognize that darn style anywhere.

so it's just you

Just updated my Firefox to v18 and it's lagging for me.

im not having any problems, must be something your end, like an addon or something? have you tried restarting your pc?

-EDIT-
if anything, it's running faster with the new update (at least it feels faster)

No problem here, but since this update, I started to use Waterfox.

I use Pale Moon instead of Firefox. It is basically the same but it uses some compiler optimisations to increase performance on Windows, as well as removing or omitting unnecessary functionality that slows the browser down (such as accessibility features that most people won't need, and some recent additions like the social network integration stuff which is pointless when you can simply go to the services' website if you so desire, and developer tools which can likely be better replaced by third party add-ons anyway). This is currently based on a slightly older Firefox code base with security patches ported back into it, so you won't get the latest stuff like the Ion Monkey javascript engine, but this may be a good thing as the engine is very new and will probably take a few versions from now to become properly stable (or at least this is the reasoning of the developer behind Pale Moon as I understand it, for not making a new build for the current code base, among other reasons).

I don't know if using this would help your current situation, but I recommend Pale Moon in any case, if you want to stick with something Firefox based.