Hello there,

Duplicate Session Restore files

Firefox may be be slow to respond or hang if multiple copies of its Session Restore file have been created:

  1. Open your profile folder:
         * (Firefox 3.0 and 3.5): See How to find your profile 
        1. (Firefox 3.6): At the top of the Firefox windowOn the menu bar, click on the Help menu and select Troubleshooting Information.... The Troubleshooting Information tab will open.
        2. Under Application Basics, click on Open Containing FolderShow in Finder. 
  2. From the menu at the top of the Firefox windowbar, select FileFirefox and then select the ExitQuit FirefoxQuit menu item.
  3. Locate and delete the sessionstore.js file and any copies, such as sessionstore-1.js, sessionstore-2.js. 

and:

Spybot S&D's "Immunize" feature can add a large number of entries into the Firefox cookie configuration file. This can cause slowdown while switching tabs.

  1. From the menu at the top of the Firefox window, select File and then select the Exit menu item.
  2. Open Spybot S&D.
  3. Click the Immunize icon on the left side of the window.
  4. Right-click in the Immunization list and choose Deselect all from the context menu.
  5. In the Firefox section, put a check mark next to each item.
  6. Click Undo at the top of the window.

If those fixes don't resolve your issue, you might want to scan your computer for malware. Malware is often the problem when experiencing lag and other rare events. Troubleshoot Firefox issues caused by malware

I can get as far as opening the Firefox directory, but don't see anything that says FileFirefox in there.

I'm running Vipre from Sunbelt Software and it shows no malware.