You have done this, that was the ESET Scanner.

You need to go in and UNINSTALL all those extra programs you used; Combofix, vundofix, Avenger, SmitFraudFix. KEEP Malwarebytes Anti-Malware and Spybot. Also keep the ATF-Cleaner. Don't worry about the Microsoft® Windows® Malicious Software Removal Tool, for whatever reasons many cannot run this tool.
To uninstall combofix do the following;
Click START then RUN
Now type Combofix /u in the runbox and click OK. Note the space between the X and the U, it needs to be there.
When shown the disclaimer, Select "2"
I cannot stress enough here again for others who may be reading this that Combofix is a powerful tool intended to be used under the guidance and supervision of an expert, not for private use. Using this tool incorrectly could adversely impact your system and prevent it from ever starting again.
One of the things that shouldn't be done is use this tool over and over, it should be used one time unless directed to do it again. When that is done it is usually recommended that the original be removed and a new copy downloaded if needed again.
Please remove it from your system.
VundoFix and SmitfraudFix are also infection specific tools, indicated when these two infections are present but not to be used for general cleaning of the computer.

These days Malwarebytes' Anti-Malware is the tool most often recommended as a FIRST step because it updates frequently (often times DAILY) AND it does remove many, many infections including Vundo infections.

Now since the problem only happens with Firefox AND you could not use the ATF Firefox option then this says to me that your copy of Firefox is probably infected and very likely corrupted. You said you are using Firefox 2 so it is out of date. Current version is version 3.0.3.
I hate to have you download a new copy before getting that infection out of there and risk having that one infected too so let's try to see if we can get that cleaned out.

Update the MBA-M program, then download CCleaner.

Shut down completely, disconnect the internet cable from the computer this way the computer cannot go online.
Then reboot to Safe Mode
1. Restart your computer.
2. When the machine first starts again it will generally list some equipment that is installed in your machine, amount of memory, hard drives installed etc. At this point you should gently tap the F8 key repeatedly until you are presented with a Windows XP Advanced Options menu.
3. Select the option for Safe Mode using the arrow keys.
4. Then press enter on your keyboard to boot into Safe Mode.

Once the computer is in Safe Mode then first run the ATF-Cleaner, again do both clean up options, first IE and then Firefox.

Next run the CCleaner on the default cleaning options, which is exactly how it will be when you open the program. It will scan the computer, list files which can be removed. Let it remove all it finds.

Next run a Full system scan with MBA-M and allow it to clean all it finds.

Shut down the computer.
Re-attach the internet cable to the computer and reboot to normal mode.
Run a new HJT scan and post back here with the MBA-M log and the HJT log.
Judy