I take it you are posting from a different computer.

First, let's make sure the computer is okay.

Perform a System File Check to fix corrupted system files

Win 7, 8, 10, Vista: https://support.microsoft.com/en-us/kb/929833 Win XP: https://www.microsoft.com/resources/documentation/windows/xp/all/proddocs/en-us/system_file_checker.mspx?mfr=true

Wiki - Windows 10 System File Check http://answers.microsoft.com/en-us/windows/wiki/windows_10-update/system-file-check-sfc-scan-and-repair-system-files/bc609315-da1f-4775-812c-695b60477a93

Some problems occur when your Internet security program was set to trust the previous version of Firefox, but no longer recognizes your updated version as trusted. Now how to fix the problem: To allow Firefox to connect to the Internet again;

• Make sure your Internet security software is up-to-date (i.e. you are running the latest version).
• Remove Firefox from your program's list of trusted or recognized programs. For detailed instructions, see

Configure firewalls so that Firefox can access the Internet. {web link}

Start your Computer in safe mode with network support. Then start Firefox. Try Safe websites. Is the problem still there?

http://encyclopedia2.thefreedictionary.com/Linux+Safe+Mode Starting Any Computer In Safe Mode; Free Online Encyclopedia

Thanks Fred! Yes, I'm posting from a different computer.

I did run sfc (it took a long time!) but that didn't change things. I also ran chkdsk in case there was a bad sector on the drive but no errors were found.

I use Webroot SecureAnywhere and you're right, when I update Firefox I have to allow it to connect to the Internet all over again. I did that and it didn't help.

Bear in mind, it's not that Firefox won't connect to the web. The program refuses to launch, and so does Chrome, Opera and Internet Explorer.

I had Firefox working earlier this morning. Everything looked perfect. Then I opened a new tab and it froze. I used Task Manager to End Program. At this point Firefox was using about 250,000kb. Firefox disappeared from the list of processes. When I tried to launch Firefox again (which used to work last week) the program choked at 8020kb and never launched. I've tried this over and over again. The only way to get Firefox to launch properly after this happens is to reboot. Then I go through the same scenario all over again.

One more thing, I'm able to launch the Avant browser with no problem. Perhaps that's a clue. Why would Avant launch but not Firefox, Chrome, I.E., Opera?

I guess I could start using Avant but I prefer Firefox and it's been fine for years.

I don't know if this is helpful but I made two screen captures. One is from the moment after Firefox crashed. It was using 395,844kb, which is normal.

After I killed the process I tried to relaunch Firefox. Before Friday, this worked fine after a Firefox crash. You can see that only 8,024kb managed to load but the browser never launched. This happens with other browsers as well.

Somehow the Firefox program becomes "tainted" or "contaminated" after the crash and nothing I do will get it to launch again. I have to reboot. Then (sometimes) I can get Firefox working. It's okay for a couple of minutes while I check a few sites. Then, unexpectedly, it freezes up. The mouse doesn't move. I have no choice but to kill the process. Obviously, going through this routine isn't helping. I'm going around in circles.

Do a malware check with several malware scanning programs on the Windows computer.

• https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-caused-malware

Please scan with all programs because each program detects different malware. All these programs have free versions.

Make sure you update each program to get the latest version of their databases before doing a scan.

• Malwarebytes' Anti-Malware:
  http://www.malwarebytes.org/mbam.php
• AdwCleaner:
  http://www.bleepingcomputer.com/download/adwcleaner/
  http://www.softpedia.com/get/Antivirus/Removal-Tools/AdwCleaner.shtml
• SuperAntispyware:
  http://www.superantispyware.com/
• Microsoft Safety Scanner:
  http://www.microsoft.com/security/scanner/en-us/default.aspx
• Windows Defender:
  http://windows.microsoft.com/en-us/windows/using-defender
• Spybot Search & Destroy:
  http://www.safer-networking.org/en/index.html
• Kasperky Free Security Scan:
  http://www.kaspersky.com/security-scan

You can also do a check for a rootkit infection with TDSSKiller.

• Anti-rootkit utility TDSSKiller:
  http://support.kaspersky.com/5350?el=88446

See also:

• "Spyware on Windows": http://kb.mozillazine.org/Popups_not_blocked

You might be experiencing a problem with the Malwarebytes Exploit Protection feature.

• Malwarebytes: turn off Real-Time Protection -> Exploit Protection
• https://forums.malwarebytes.com/topic/209334-install-3222018-and-firefox-5230-crashes/

If the above does not help, Start your Computer in safe mode with network support. Then start Firefox. Try Safe websites. Is the problem still there?

http://encyclopedia2.thefreedictionary.com/Linux+Safe+Mode Starting Any Computer In Safe Mode; Free Online Encyclopedia

Thanks for the tips! I already use MalwareBytes Anti-Malware and I already ran Kaspersky TDSS Killer -- twice. AdwCleaner wouldn't load under XP. Maybe I got the wrong version?

ComboFix wouldn't install either.

I tried installing a fresh version of Kaspersky TDSSKIller but it wouldn't install. I have a feeling this software isn't intended for Winows XP SP3 32-bit.

Kaspersky Free Security Scan started to install but it tried to delete Webroot (which I pay good money for) so I had to abort the installation.

I did manage to load SpyBot Search & Destroy. It found 280 "problems" but these were mostly recent files lists and Flash Player text files. Nothing was marked as malware, spyware or adware. All 280 items had a low threat level.

I'm running Microsoft Safety Scanner now. It may take a while.

Any other ideas in the meantime?

Did you check for issues caused by the Malwarebytes Exploit Protection feature like I posted above in case you use this software?

Yes, I followed that link. Of course, I've been using Malwarebytes for years so I don't think that's the problem. I even turned MalwareBytes completely off but I still had the same issue with the browser.

Microsoft Safety Scanner just now found 4 "infected files" but I probably won't know what they are until it finishes scanning. It has been running for an hour and 45 minutes and the progress bar has barely moved so I'll have to leave it going overnight and resume troubleshooting in the morning.

Thanks again for your help!

You said you were crashing. Is there any crash reports please ? https://support.mozilla.org/en-US/kb/firefox-crashes-asking-support

Thanks for the suggestion Pk. I looked up the crash reports and the most recent one is from two years ago. Maybe what I'm experiencing is more accurately called a "freeze" rather than a "crash."

When I booted up this morning I was able to get Firefox to launch. I opened a new tab to check some settings and it froze. Usually I have to kill the process in Task Manager at that point, but today I was able to close Firefox normally. That's a small improvement but it hasn't yet solved the problem.

Getting back to an earlier idea, I ran Microsoft Safety Scanner all night. It took about 12 or 14 hours. I didn't realize it was scanning not only drive C, but a few USB drives I use for backups and file storage. No wonder it took so long! It found some supposed viruses in backups I probably hadn't looked at in a decade or more. I don't think that was the problem but I'm impressed at how thorough it was.

Microsoft Safety Scanner did find and fix a couple of problems on the C drive, although that still hasn't resolved my issues with browsers failing to launch.

The other aspect of this is my inability to read PDFs. I uninstalled deleted Acrobat Reader figuring that I could always install it again but that did no good. Now I can't launch Adobe Acrobat (which I paid for) so PDFs (which I use in my work) cannot be opened.

What in the heck is wrong that affects both browsers and Adobe products? I'm not a software engineer but just from a logical perspective it seems like there's a bit of code that's common to browsers (Firefox, Chrome, Opera, Internet Explorer) as well as PDF reader.

Perhaps this is a question for Microsoft.

FredMcD said

Start your Computer in safe mode with network support. Then start Firefox. Try Safe websites. Is the problem still there?

http://encyclopedia2.thefreedictionary.com/Linux+Safe+Mode Starting Any Computer In Safe Mode; Free Online Encyclopedia

DancinDave said

scanning not only drive C, but a few USB drives I use for backups and file storage. No wonder it took so long! It found some supposed viruses in backups I probably hadn't looked at in a decade or more

Before you do anything, it's possible the report could be a false positive.

Too late to do nothing, I already let Microsoft Safety Scanner do what it wanted.

I haven't done what you suggested about trying in safe mode yet because of what I just discovered...

In addition to Firefox, Adobe Reader, etc., I found I could not launch MS Word. (I'm trying to get some work done while I'm going through this nightmare.) Word also failed to launch in the same way. It starts to load then it chokes and stops. I tried clicking a few other icons and could not get several other programs to launch. So this isn't just a browser problem, it's much bigger.

I vaguely remembered going through something like this years ago. Something about file associations being corrupted.

I found a fix on Doug's Windows Tweaks and Tips. I've been using his registry fix to get my EXE files working again. It works for a while then it doesn't. My current theory is that some kind of virus is messing with my registry. I've scanned for viruses over and over but it keeps happening.

If I'm right, then this is not a Firefox problem and I probably souldn't be posting on this board. Unless someone here has specific experience with this missing file associations problem, I'll look for help elsewhere.

Anyway, thanks for all your help, everyone!

Please just go here after reading below and they will work on your cpu for you supplying information and software to run to help recover from infection. Let the experts help. https://forums.malwarebytes.com/topic/9573-im-infected-what-do-i-do-now/

Please let us know if this solved your issue or if need further assistance.

Thanks again, Pk. I posted to the Malwarebytes forum. Waiting for a reply. I'm a paid Malwarebytes user so I hope they can help.