Just to check, does your CPU usage spike too? Try checking it with your system monitor. This used to happen to me and the problem lay with flash. You should try uninstalling flash fully using add/remove programs and then reinstalling from Adobe's website. Get the download from here:

http://get.adobe.com/flashplayer/

I hope this helps. In my case, I had done the same thing and it worked fine from then on.

Hi AdelaisAer,

First try to Turn off hardware acceleration in Firefox and "disable the hardware acceleration" in the Flash Player too :

http://helpx.adobe.com/flash-player/kb/video-playback-issues.html

http://www.macromedia.com/support/documentation/en/flashplayer/help/help01.html

also try to Disabling Protected Mode in Flash (the link is for 11.3, do the same for 11.4), see the same in "Last resort" in the next link from adobe forum http://forums.adobe.com/thread/1018071?tstart=0

thank you

Disabling Hardware Acceleration didn't really work. I'll try to just uninstall Flash and do a clean install. I'll update as I go along and see if it solves anything.

EDIT: It still does it a bit. :S

Okay, so I uninstalled and reinstalled it. That helped only for about ten minutes and it started doing it again.

I don't know what else to do. :S

Try to Downgrade to Flash 10.3 , but as the suggestions in the link said uninstall first uninstall Flash with uninstaller provided by Adobe (it is in the link) and then download and install 10.3

[the 10.3 flash is updated before 6 - 7 days(https://support.mozilla.org/en-US/forums/contributors/708573?last=48772#post-48758)]

thanks again

Actually, I think it might be FireFox, because sometimes it slows down or freezes even without me using a Flash video. Like, I'd open a link in a new tab (something simple, like TD Bank or Google) and the tab wouldn't appear and the window would freeze. :S

Try to rename or delete the files places.sqlite and places.sqlite-journal (if exists), see how to do that easily :

Firefox hangs at random times

also Delete duplicated Session Restore files

thanks again

I deleted places.sqlite and duplicate session restore files. It still seems to do it. :S

On top of this problem, a new one arises - sometimes, flash videos just randomly restart mid-way. o-O;

Guys. Wake up. Why would we go to all this trouble just to get Firefox to run properly? Why can't it just work correctly right out of the box, like Chrome? Myself and I suspect many others are just about through trying to use Firefox in its currently unusable state. The rats are jumping ship. A few more months of this level of unacceptable browser performance and you will be hanging up your hats, or rather tipping your hats in salutation as you slink off in defeat, having had your derrieres soundly thrashed up one side of the street and down the other, by Chrome. Hope you can find new jobs in this economy. By the way, I am currently using Linux Mint, it's awesome! Yet some mega-companies are trying to stem the tide and drop support for Linux. They will be left in the dust. Fair warning.

Hello anon147, you said.....By the way, I am currently using Linux Mint, it's awesome! Yet some mega-companies are trying to stem the tide and drop support for Linux..."

think if this already try to happen in firefox too !

thank you

Look for disabling ProtectedMode in the Flash player. It will eliminate the hanging. However, it replaces it with another problem, I seen before:

https://bugzilla.mozilla.org/show_bug.cgi?id=745433

mouse clicking becomes unreliable in the Flash. It just cannot handle mouse properly when controls are small (yet large enough for the human to easily point over them precisely). I had to zoom the page to make flash capturing the mouse events properly.

Developers say that it is a Flash problem but none exist when I run the Flash in IE.

Now, I have realized that my too high Windows 7 screen resolution (custom text size of 200% = 192 DPI) or DPI virtualization used to achieve that can be a problem for many video applications http://www.techrepublic.com/blog/window-on-windows/get-a-better-view-in-windows-7-by-adjusting-dpi-scaling/5404 http://msdn.microsoft.com/en-us/library/windows/desktop/dd940516%28v=vs.85%29.aspx

It seems that not only Firefox freezes, some MS products also suffer from the same, DPI virtualization, problem http://stackoverflow.com/questions/9663585/vs2010-stuck-freeze-in-any-kind-of-scrolling

And the solution used thereby, to "Disable display scaling on high DPI settings" in Firefox shortcut -> Properties -> Compatibility also fixes both the freezing and broken mouse problem! So, try FF compatibility before blaming the Adobe Flash Protected Mode. I think that it is a FF bug because it does not exist in IE and FF is an "older program".

Because it has nothing to do with firefox? Nothing else causes firefox to freeze like this and it all started going wrong when I updated flash a few months ago. If anything this is evidence of why I should ditch flash, not my perfectly good browser.

Check your not-that-good browser. How is it with flash?

Or rather, how is flash with my browser? Mozilla can't force another organisation to fix their bugs. All the more reason to switch to open standards like webGL.

Flash still causes my browser to freeze every so often. Hell, sometimes, it crashes. :/ And I already went through all the suggestions in this thread, so I think it's a problem with the Flash plug-in for Firefox.

My computer is Asus G74SX-DH72, so I wouldn't say that it's my computer that can't handle it.

I suffer the same severe Flash sluggishness on firefox using Ubuntu. Not so with Chrome. What's a bit laughable is that Seamonkey (former "bloated" Mozilla suite replaced by Firefox) runs flash better- and has been a quicker browser all-around for some time. I assume firefox code bloat/ extensions and Flash's unecessarily heavy resource appetite account for the embarrasing performance.

If you have extensions that can do things with IP addresses (my problem was Fiddler), try to disable that extension. It stopped my problems

I use and im using firefox since i had got Netscape Navigator and want to tell everyone that it flashplayer poblem! Not Firefox, because when you kill that process from the taskmanager - everything is ok! May be we need to update Flashplugin or may be we need alternative!

Does Netscape Navigator still exist? O.o

At any rate, there isn't anything Mozilla can do, it's up to Adobe to fix the problem with flash. I have the latest version but it's still not great. The alternative is the HTML5 canvas element, which alot of websites are switching over to.