Could you describe the symptoms in a little more detail:

• Do you hear the fan come on, disk drive accessing, or other indication that the system is suddenly working harder?
• Can you move the mouse pointer around or is it frozen?
• How long does it usually last, or is it so long there's no point waiting to find out?
• Any connection with plugins such as Flash on the pages where Firefox freezes?

Could you try starting Firefox in its Safe Mode? With Firefox not running, hold down the Shift key when starting Firefox.

Instead of the home page, a small dialog should appear. Click "Start in Safe Mode" (not Reset).

Any difference?

I am not sure if a fan comes on; I will pay attention next time. Yes the mouse and the rest of the computer locks up. I have tried control, alt, delete but that is locked too. Yes I have tried it in safe mode. It lasts at least 3 minutes or more. I usually get out my book or get up and come back. I have Flash set to "ask to activate". I don't think it is related to Flash on the site though. I have spent a lot of time on the Mozilla trying all the suggestions with no results.

Could you test with these plugin settings:

Set to "Always Activate":

• Content Blocker Extension
• Online Banking Extension
• Virtual Keyboard

Set to "Ask to Activate":

• QuickTime

Set to "Never Activate" (i.e., temporarily disable completely):

• Shockwave Flash

If you can't get to the Add-ons page after starting Firefox normally, you can start up directly to that page using the search box on the Windows start menu, type or paste the following and press Enter:

firefox.exe "about:addons"

Any difference?

You want the first 3 to be "always activate". QuickTime: ask to activate. Flash: Never Activate

Is this correct? That is what I did.

Yes, and... No improvement? Some improvement?

Start your Computer in safe mode with networking. Then start Firefox. Try Safe web sites.

Starting The Computer In Safe Mode;
Free Online Encyclopedia

Reply to Jscher 2000. No that didn't do it. It just locked up again. Darn!

Reply to Fred McD. The problem with safe mode is that it does this randomly. The site it just locked up on is one that I usually use every day. There doesn't seem to be any rhyme or reason as to the sites that it locks up on. I can click on a link or links for a period of time and all of a sudden it locks up.

Sorry to hear that. So, the next two diagnostic approaches are as follows:

Create a new Firefox profile

A new profile will have your system-installed plugins (e.g., Flash) and extensions (e.g., security suite toolbars), but no themes, other extensions, or other customizations. It also should come with completely fresh settings databases and a fresh cache folder.

Exit Firefox and start up in the Profile Manager using Start > search box (or Run) -- type or paste the following and press Enter:

firefox.exe -P

Don't delete anything here.

Any time you want to switch profiles, exit Firefox and return to this dialog.

Click the Create Profile button, assign a name like March4, and ignore the option to change the folder location. Then start Firefox in the new profile you created.

Does Firefox run more normally in the new profile?

If so, it sounds like a settings problem. If not, it could be corruption of Firefox's program files. See the "Clean Reinstall" section below.

When returning to the Profile Manager, you might be tempted to use the Delete Profile button. But... it's a bit too easy to accidentally delete your "real" profile, so I recommend resisting the temptation. If you do want to clean up later, I suggest making a backup of all your profiles first in case something were to go wrong.

To keep the new profile and migrate data, check out this article: Recover important data from an old profile. We can go over that in more detail as needed.

Clean Reinstall

(1) Download a fresh installer for Firefox 36 from https://www.mozilla.org/firefox/all/ to a convenient location. (Scroll down to your preferred language.)

(2) Exit out of Firefox.

(3) Rename the program folder

(32-bit Windows folder names)

C:\Program Files\Mozilla Firefox

to

C:\Program Files\OldFirefox

(64-bit Windows folder names)

C:\Program Files (x86)\Mozilla Firefox

to

C:\Program Files (x86)\OldFirefox

(4) Run the installer you downloaded in #1. It should automatically connect to your existing settings.

When starting Firefox, you may need to use the profile manager to switch back to your regular profile.

Does Firefox run any better with the new program files?

Note: Some plugins may exist only in that OldFirefox folder. If something essential is missing, look in these folders:

• \OldFirefox\Plugins
• \OldFirefox\browser\plugins

To Jscher: In answer to your question yesterday; the fan did not go on when it locked up.

Okay I created a new profile. But none of my passwords or add ons are there. Do I have to download all of my add ons again. What do I do about my passwords?

I did a clean install in February. I think everything was there then but still had the problem.

Hi Budieus, you can copy individual settings files such as bookmarks and passwords to the new profile, but add-ons probably need to be reinstalled from the source.

If you paste the following into the start menu search box or into the address bar of a Windows Explorer window, you can find your profile folders for possible copying from one to another:

%APPDATA%\Mozilla\Firefox\Profiles

This article describes which files have which stuff in them. Please make sure Firefox is not running when you replace a file. Recover important data from an old profile

Is there any way to know whether the new profile actually is problem free at this point (i.e., is there any reliable way to re-create the problem)?

No I don't know of anyway to tell if it is problem free or re-create the problem because it seems to be random sites. It is faster though.

I really appreciate all the time you have spent trying to solve this. It looks like I have most things back like passwords and some bookmarks. I have the add ons except Desk cut doesn't doesn't work. I went to the site and downloaded it again and got the message that it doesn't work with Firefox 36. However on my old profile I have Firefox 36 and it works with that. It is an older version from 2012. I really miss that! The new profile so far has not locked up. I forgot to mention that I have Vista not windows 7. Does that make a difference?

As far as Firefox is concerned, I think Windows 7 and Vista look the same, but I wouldn't be surprised if the population of testers has many more Windows 7 users than Vista users and this could cause Vista-specific issues to be missed in testing.

I haven't heard that deskCut doesn't work in Firefox 36. At what point do you get that message? The reviews indicate issues with one of the settings, but also discuss a workaround (going into the extension's Options to reset the path): https://addons.mozilla.org/firefox/addon/deskcut/reviews/

I think I solved it; I hope. I went to the desk cut web add-ons page. The developer suggested to set the path to "find". So far it worked.

I guess that is what you found too. That should solve the problem. Thanks again!

For two weeks now Firefox has been locking my computer. NOT on start but maybe 5 to 10 minutes after. I've followed the above troubleshooting/corrective actions and still have the problem. The computer does NOT lock up using Google Chrome. I prefer using Firefox, however. I have a Dell Inspiron 1545 laptop, using Windows Vista 64 bit I am going to try creating a new profile and see if that works. If it doesn't, what would I need to do?

Well, that didn't work. Still locked up. Anyone have other suggestions?