What is the file size of the sessionstore.js file?

You can use this button to go to the Firefox profile folder:

• Help > Troubleshooting Information > Profile Directory: Show Folder (Linux: Open Directory; Mac: Show in Finder)

Did you create a new profile or did you reset Firefox?

Hi there. It is currently 171 KB (not the 427 KB that I originally posted - I was looking at the wrong file). I created numerous new profiles as well as uninstalled and reinstalled FF with a clean profile. I haven't reset it as I just assumed uninstalling and reinstalling would work the same way, but I will try that if it does something other than that.

Okay, so went back and uninstalled FF 27.0.1 and then reinstalled 24 on a fresh profile and it still does the same thing. Freezes every 20 seconds for 5 seconds if I have numerous tabs up, ugh. Could the latest flash update cause something like this?

Boot the computer in Windows Safe Mode with network support (press F8 on the boot screen) as a test to see if this helps.

Safe mode didn't help either, still freezes every 20 seconds with tab usage.

Do you maybe have a (pinned) website that is always present?

I got almost crazy troubleshooting this, I almost bought a new video card, but then it turned out that it just was a specific pinned site that caused a freezing every 20 seconds (in my case www.di.fm).

Do a malware check with several malware scanning programs on the Windows computer.
Please scan with all programs because each program detects different malware.
All these programs have free versions.

Make sure that 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: Home Page:
  http://www.microsoft.com/windows/products/winfamily/defender/default.mspx
• 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

No, I don't have a site pinned, but thanks for the suggestion, Peter_FB and thanks for all of your help, cor-el. I have already scanned with Malware Bytes yesterday, but will try the rest in the next few days. I can understand that heavy usage with tabs could cause FF to freeze a lot (which it never has for me since '09), but it is it the fact that it is freezing always every 20 seconds on the dot that baffles me.

Okay, since an upgrade to FF 28, I am not getting freezes like I was and this is with a TON of tabs. Also, I noticed an improvement in overall FF performance after removing Spotify background programs (Spotify Web Helper in particular). I found no viruses or spyware either. Hopefully this continues and no more freezes! Thanks again for your help!

Are there possibly numbered sessionstore-##.js files in the profile folder?

What is the file size of the sessionstore-##.js file?

You can check for problems with the sessionstore.js and sessionstore.bak files in the Firefox profile folder that store session data.

Rename (or delete) the sessionstore.js file and possible sessionstore-##.js files with a number and sessionstore.bak in the Firefox profile folder.

• Help > Troubleshooting Information > Profile Director: Show Folder (Linux: Open Director; Mac: Show in Finder)
• http://kb.mozillazine.org/Profile_folder_-_Firefox
• http://kb.mozillazine.org/Multiple_profile_files_created

Deleting sessionstore.js will cause App Tabs and Tab Groups and open and closed (undo) tabs to get lost and you will have to recreate them (make a note or bookmark them if possible).