hello remmeler, please Update Firefox to the latest release & also update all of your plugins and see if this already addresses the issue...

Which security software (firewall, anti-virus) do you have?

A possible cause is security software (firewall,anti-virus) that blocks or restricts Firefox or the plugin-container process without informing you, possibly after detecting changes (update) to the Firefox program.

Remove all rules for Firefox and the plugin-container from the permissions list in the firewall and let your firewall ask again for permission to get full unrestricted access to internet for Firefox and the plugin-container process and the updater process.

See:

• https://support.mozilla.org/kb/Server+not+found
• https://support.mozilla.org/kb/Firewalls

I checked and I was using the latest Firefox on the Windows 7 system, but I did update it on the XP system after madperson's suggestion.

I am running the standard windows firewall and avast on both systems that automatically update (to answer the second suggestion) There are no rules in the firewall settings for Firefox.

There are some for WinTV and Win Live Sync and diagnostics and UPnP framework and remote assistance and Cyberlink Power DVD and file and printer sharing and Google Talk and Hardware Monitor Pro and file and printer sharing, but those all look pretty standard.

I ran the same routine on both systems at the same time and viewed different videos randomly and duplicated on the XP system until it slowed down on playback on Win 7. I continued on the XP system and it did not slow down.

Try to create a new profile as a test to check if your current profile is causing the problems.

See "Creating a profile":

• https://support.mozilla.org/kb/profile-manager-create-and-remove-firefox-profiles
• http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Profile_issues

If the new profile works then you can transfer some files from an existing profile to the new profile, but be careful not to copy corrupted files.

• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

I think my easiest option is to uninstall Firefox completely and just re-install after a reboot. What do you think?

You can still first give a new profile a try to see if that helps.

If not then your problem may be more likely caused by security software (firewall, anti-virus).

I think I took the easy way out. I just uninstalled Firefox and then downloaded and reinstalled and just added DownloadHelper. It seems to have worked. I just did an extended test and no slow down.