Uhoh... This may be caused by malware. Malfunctioning malware... Let's hope it's not. It's possible that you are having a problem with some Firefox add-on that is hindering your Firefox's normal behavior. Have you tried disabling all add-ons (just to check), to see if Firefox goes back to normal?

Whenever you have a problem with Firefox, whatever it is, you should make sure it's not caused by one (or more than one) of your installed add-ons, be it an extension, a theme or a plugin. To do that easily and cleanly, run Firefox in safe mode (don't forget to select Disable all add-ons when you start safe mode). If the problem disappears, you know it's from an add-on. Disable them all in normal mode, and enable them one at a time until you find the source of the problem. See this article for information about troubleshooting extensions and themes and this one for plugins.

If you need support for one of your add-ons, you'll have to contact its author.

If the problem does not disappear when all add-ons are disabled, please tell me, so we can work from there. Please have no fear of following my instructions to the line, as all can be easily undone.

Hi Morbus,

Thanks so much for responding. I really hope you'll be able to help me out. This has been going on for days, and it's driving me nuts. And it only seems to be getting worse...

Starting this afternoon, my Firefox has developed a whole new bad habit. It still crashes nearly every time I try to log in to any site requiring me to enter a user name and password. For some reason, if I click "remember me next time" or its equivalent, I've found I can usually sign in. A great quick fix for now, but I'm not really comfortable being automatically signed in to so many different sites, as I'm not the only one who uses my computer.

But now, to make matters worse, even when I do sign in someplace, Firefox begins to slow down. For instance, if I'm typing an email (or even writing this response - I had to go to my wife's laptop and start over!), the cursor will lag behind my typing, and then eventually Firefox will just freeze, after 2-3 minutes or so. The program becomes unresponsive, and I have to close it through Task Manager. Not a good scene.

I tried running Firefox in safe mode with all my add-ons disabled, and I still had the same issues. I've been running daily full scans with AVG Free, Malwarebytes, and Ad-Aware, as well as the malicious software removal tool issued by Microsoft every month for Windows. All of those programs have found tracking cookies, even after I've cleared my recent history in Firefox. Getting rid of the tracking cookies hasn't helped, though. I'm afraid they're a symptom, rather than the cause.

A couple days ago, AVG did find a virus called _ex-f.exe, which I deleted. As recently as last night, the Windows malicious software removal tool found another virus, Win32/Alureon.H, and says it got rid of it.

I suspect that malfunction mal-ware is the problem, as well. Beyond the steps I've already mentioned, though, I don't know what else to do about it. I'm hoping you know what to try next.

I don't know if this is relevant, but I figured I should mention that I downloaded the latest version of Google Chrome a few days ago, just out of curiosity. It didn't function properly - websites would appear to load without any problem, then disappear after a couple seconds, leaving an "Aw, Snap" error message. I uninstalled Google Chrome that same day, which is also the same day that I started having these problems.

Any advice on what to do from here would be greatly, greatly appreciated. Thank you for taking the time to help!

Well, tracking cookies are privacy holes, not viruses. It may well be that this problem is due to a virus, but let's rule out a corrupted or misconfigured profile first. Can you please try it in a new (temporary) Firefox profile and see if the issue is still present? See this article to know how to create a new Firefox profile. Please report back the results.

Hi Morbus,

I created a new Firefox profile, but unfortunately I still had the same problem. What's our next move?

Thanks again!

Try reinstalling Firefox. No data will be lost (as long as you don't instruct the uninstaller to delete your private data). You can get the latest version (the one you're using) from getfirefox.com, as always. I doubt that will fix the problem, unfortunately, but let's try that first, since the other troubleshooting methods are more complex.

No such luck, I'm afraid. Same old problems came right back again.

Well, what I would do, in your case, is start Windows in safe mode and see if the problem disappears. I can't say for sure, but I think you need to press F8 when your computer is booting up. It will start windows in safe mode, which will disable most services and applications. If it works, you know it's one of those things that got disabled by safe mode that is causing the problem. This may be any thing, but only you can find it, since no one else has physical access to your computer.

Sorry for the slow response. I've started Windows in safe mode with networking enabled, and I've had some mixed results. The first time I started up Firefox, it let me sign into Gmail, but then it froze a moment later and needed to be forced to quit.

Every subsequent time I've opened Firefox, though, I've been able to sign into Gmail and other sites without any trouble, and then continue to browse without experiencing any more freezes or crashes.

I'm willing to consider that first freeze a fluke and say that the problem has gone away while Windows is in safe mode. At the very least, I haven't had any incidents of Firefox crashing while I'm trying to log in to Gmail or any other site. So that's something.

Like you said, if the problem is in one of the applications that's disabled by safe mode, only someone with physical access to my computer can actually identify the source of the issue. But do you have any advice on how I might proceed from here/where to start looking?

Thank you again for your help!

Well, I suggest you check any unnecessary applications that are running at startup. Often people forget (or simply don't know) about startup programs, and are running software that they don't know is running because it automatically starts itself on startup. Startup programs are not started on safe mode, of course, so the culprit may be there. I doubt it though. I think your best bet is to check for malware. To scan for malware, install, update and run these programs in this order. They are all free for personal use, but some have limited functionality in their "free mode", but the features you'll miss are not really needed to find and remove the problem you have. Remember that not all programs detect the same malware!

• Malwarebytes' Anti-Malware - malwarebytes.org/mbam.php
• SuperAntispyware - superantispyware.com
• AdAware - lavasoftusa.com/software/adaware
• Spybot Search & Destroy - safer-networking.org/en/index.html
• Windows Defender - microsoft.com/windows/products/winfamily/defender/default.mspx
• Dr. Web Cureit - freedrweb.com/cureit

I also suggest you contact someone experience with these things, if you are not comfortable doing the fixing yourself.

It took me a while to run them all, but I'm cautiously optimistic - that seems to have done the trick! Just the fact that I could sign in and write this reply from my own computer is something that I haven't been able to do for weeks.

Thank you for introducing me to all those programs - a few of them I'd never heard of before, but they really seemed to catch things that my usual routine of AVG, AdAware, and Malwarebytes was missing. Most notably, Dr. Web Cureit found a Trojan embedded right in one of Firefox's data files. After getting rid of that infection, Firefox seems to be working normally again.

Thank you so much for taking the time to help me out! I really appreciate all your advice. I'm probably going to hold my breath every time I try to log into Gmail for a little while, but as of this evening, everything seems to be working perfectly!

I had the same problem. I deactivated Kaspersky Password Manager Autofill and the problem stopped.