Try the Firefox Safe Mode to see how it works there. The Safe Mode is a troubleshooting mode, which disables most add-ons.

(If you're not using it, switch to the Default theme.)

• You can open the Firefox 4.0+ Safe Mode by holding the Shift key when you use the Firefox desktop or Start menu shortcut.
• Or use the Help menu item and click on the Restart with Add-ons Disabled... menu item while Firefox is running.

Don't select anything right now, just use "Continue in Safe Mode." To exit the Firefox Safe Mode, just close Firefox and wait a few seconds before using the Firefox shortcut (without the Shift key) to open it again. If it is good in the Firefox Safe Mode, your problem is probably caused by an extension, and you need to figure out which one.

Please follow the Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems article for that.

When you figure out what's causing your issues, please let us know. It might help other users who have the same problem.

Hi Baldape,

I think I may have mentioned in other threads where you have posted: it is NOT a good idea to use an old insecure version of Firefox.

Clearly you have taken such a decision aware of the security risks, and may have mitigated them with some form of virtualisation or sandboxing, but I add this note for the benefit of other readers of this thread.

• see Install an older version of Firefox

In fact I would recommend even to you, that unless you know of a very specific incompatibility you too would be better using Firefox 13 or later.

Any set of interactive software used with Firefox can have some impact on speed and memory use. Possibly you have a set that is problematic and maybe any problems are synergistic and particularly bad with that combination.

I did notice from a quick web search some users reporting Firefox problems when Advanced System Care is in use. Security software often needs setting up correctly so as not to cause problems.

A quick method is using Firefox 13's new reset feature. The older method (personally I prefer it anyway) is to test Firefox temporarily in a new clean profile. To create and use a new clean profile

1. follow instructions in Troubleshoot and diagnose Firefox problems_8-make-a-new-profile
2. then look for any add-ons and plugins after starting in the new profile and remove anything other than the default theme.

If you have problems in the clean profile then look at security software and firewall settings.

• Configure firewalls so that Firefox can access the Internet
• also look at Server Not Found - Troubleshoot connection problems
• presumably you have tried IE and that has no problems ?

One Firefox 13 problem is with FlashPlayer, but there are workarounds for that, and I am sure a more permanent solution will be provided shortly. Lets deal with that later on if we need to.

Other advice is

• look at and follow advice in the article firefox hangs or is not responding - How to fix
• and send performance data to Mozilla to help improve Firefox

BETA As a use stratagy.

Have you considered instead of downgrading to older versions upgrading to newer versions: Beta or even Aurora. Assuming they work ok for you the big advantage is that after you have been on Beta for six weeks you always then have a safe secure and tested downgrade option should any new beta release prove problematic just drop to the standard Release. Something that you will have already been using for its six week stage as a Beta release.

No not the beta to much work and there not always stable but I'm thinking about temporally switching to SeaMonkey and yes because I sandbox FF I'm much safer than the average FF user but part of the reason I rolled back was to see if really is just a v13 problem which I think it may not be and FYI IE works just fine as far as I can tell but the Advanced System Care isn't so much security software as its maintenance kinda like CCleaner but like SpyBot it has cookie/script blocking feature and I would have to get a hold of them to find out how to remove or disable the setting changes it can make to the browsers I'm wondering if the other people who are having the same/similar problem also have Advanced System Care? If so then there's the likely culprit for this problem.

When you rollback depending on how you do it you may make profile changes, or even do a complete clean re-install and so have a new profile, that could be a factor sometimes.

Whatever sandboxing or virtualisation you are using is another factor that could potentially generate problems. Also I am not sure running at least three sets of software that may have script blocking is a good idea, could that not cause conflicts. Avast & Malwarebytes pro may conflict, I doubt they are expected to be used together. see next post, link suggests Malwarebytes pro may be configured to run with other AV

It is possible to run multiple versions of Firefox. An easy way to do that on Windows is to use Firefox Portable. Why not install and try Firefox portable see how that runs ?

• http://portableapps.com/apps/internet/firefox_portable

When any change is made, it is not always obvious what the critical factor is.
I have previously seen users say something does not work in Browser A but does work in Browser B whilst others say it does not work in Browser B but it does in C only for the circle to be completed with a statement C does not work A does. It turned out it was simply that cookies and cache needed clearing. Anyone changing browsers for a new one starts with a no cookies and nothing cached.

We can be fairly certain most users have no problems with lagging in Firefox 12 or 13 and the problem is likely to be something to do with your individual set up. Your set-up is rather complicated and I suspect quite likely to result in conflicts, race conditions &/or incorrect blocking/locking.

The troubleshooting steps take rather a bit of effort, but unless you try them you are not likely to get to the bottom of this problem.

"No not the beta to much work and there not always stable"

Switching to Beta is easy.
As easy as downgrading or upgrading, and has the advantages that you do not miss new features or security patches. Beta rarely causes any kind of stability or other problem that the main Release does not get, because it is the final testing before it becomes the Release. Changing, adding and removing of features is usually done in the Nightly and Aurora Releases.The Beta channel is really nearer to what may normally be referred to as a Release Candidate.

Mlwarebytes Pro was meant to run along side antivirus programs like Avast which if you read here works just fine with it: http://forums.malwarebytes.org/index.php?showtopic=108719

http://forum.avast.com/index.php?topic=95381.0 And I never had any problems myself with the two of them although there were issues in the past with Sandboxie and Avast but the maker of SB quickly fixed this bug. And FYI I did clear my cookies and browser cache with CCleaner and I only have 3 security programs on my system Avast,Malwarebytes Pro and Sandboxie and when it did freeze up it even happened unsandboxed so we can pretty much put Sandboxie out the equation. I'm thinking it might be one or more of my extensions because a few are out of date at least 8 months that or it the Advanced System Care immunization feature much like how SpyBot's immunization can cause problems I'm sure AVC immunization can also cause problems although Ive never had any problem with its immunization feature in the past.

Installing and running Firefox portable seems he quickest and easiest way of getting a clean profile Firefox version installed that you can test for freezes and lagging.

In your situation I suspect asking others will not get you very far they will not be configured the way you are. In my opinion you need to troubleshoot.

I only have 3 security programs on my system Avast,Malwarebytes Pro and Sandboxie

That may still be unusual and maybe one too many.

You also have script blocking

Advanced System Care isn't so much security software as its maintenance kinda like CCleaner but like SpyBot it has cookie/script blocking feature

1. no-script
2. SpyBot
3. Advance System Care
4. (I did not try to check out features of your other security applications)

And it is not inconceivable that cleaner utilities are messing-up settings of the scriptblockers, security applications or some of Firefox's files or caches.

Well Sandboxie isn't antimalware/antivirus it just Sandboxes my browser or email software by the way do you think that corrupt bookmarks could cause this to happen and what are some of the signs of corrupt bookmarks?

Did you try safe mode, like mixalis88 suggested?

I'm going to try that next after the 15th or if FF v11 freezes up on me one note the Adobe Flash player crashed on just couple of hours ago although I had around 20 tabs open on YouTube but I wasn't playing videos in each tab all but one was paused Ive done this many times before and never ran into any major problems but Chrome gave me trouble before on YouTube.

Lets try to get Firefox working properly without freezing, as a first step. Try later to find out what factor or combination of factors is causing the problem.

Why not try to make this as simple and easy as possible. There are several methods which allow you to troubleshoot by test running Firefox with fewer software extensions.

1. Safe Mode
   Is worth trying, amongst other things it disables add-ons but NOT plugins
2. A new clean profile
   If you use a clean profile you can also have plugins uninstalled from that profile, Without affecting the browser profile you normally use
3. Firefox portable
   That could give you a completely clean separate install of Firefox. It installs as an additional browser. You can make changes to that, or even run a totally different Firefox browser version, without affecting your ordinary main installation

BOOKMARKS If you use

• Fx 13 reset feature OR SafeMode - - they (by default) retain the existing bookmarks.
• a clean profile [method 2]
  you may ensure a clean almost empty bookmarks database is used.
  (Whilst keeping the original bookmarks safe in the original profile. )
• Firefox Portable
  that may be installed & started with just the default bookmarks, not your ordinary set.
  The bookmarks are kept separate from your ordinary Firefox bookmarks.

Flash Player
There certainly are some known issues with Firefox 13. As I mentioned earlier I would rather deal with this problem later. If Firefox is already hanging and freezing what is the point in trying to run FlashPlayer or sort out FlashPlayer problems.

I personally spoke to several people the last week and only a few of them are having this problem (in fact one them was a computer technician) but they all have one thing in common and that's they all have Avast antivirus on there PCs. Note: I was going to wait till the 16th to give my verdict but I had restore my PC back on the 9th because I installed a bad program/ran plus with this news I heard from people I know I'm almost a %100 positive this a Avast&Firefox v13 issue.

Thanks for the update!

Actions speak louder than words. Instead of repeatedly asking different people and different questions why not try some testing and troubleshooting.

For instance if you think it is an Avast & Fx13 issue try with Avast installed and uninstalled and compare the results. If others then repeat and confirm the results you may be able to report the problem and ask for a fix.

I have not personally noticed a large numbers of posts complaining about Avast. I have also quickly glanced at their support forum, a few posts mention Firefox.

Suggestions maybe try

1. Asking on their Avast support forum http://forum.avast.com/ do others have problems with Firefox lagging or not ?
   but note that does not prove a causative correlation, you are selecting from a set of Avast users with a problem of Firefox lagging !
2. Observe of thousands of input feedback posts on fx 13 issues only a handful even mention Avast
3. same on this forum, start a new thread asking. Consider using a new tile such as
   • Avast users: Help does your Firefox lag and freeze ?
   • again remember some proportion of users will have lags and use Avast, that is why I say tests are needed instead of just questions.
4. you could also edit the title of this post to include the word Avast.
5. If you get responses you and others could test the theory
   • BUT care, it could result in lags due to malware if Avast is off
     a solution may be to install free Windows MS AV whilst you test
     I do not notice freezes & lags using Windows free AV BTW

Well I just made a new post about this topic here:

https://support.mozilla.org/en-US/questions/932088