hello jetbluez06, maybe it's an issue with the protected mode that adobe has introduced in its flash plugin for firefox - you could try if downgrading to flash 10.3 (which is still supported) or disabling protected mode makes a difference.

Make sure that you install a Anti-virus and firewall provider, the simplest firewall provider is windows firewall, but the best in my opinion is AVG!

Once you have A proper Firewall service, try and download AVG for anti-virus which is free, but the payed one is better.

deleted email address - moderator

also, have you tried the best internet speed tester out there? Speedtest, I hope that I helped!

P.S. It could be your Adobe Flash player, if you want to downgrade you can here: Adobe Flash download

I disabled protected mode as described and it worked perfectly. Now Firefox gave the same speedtest results as Chrome and IE. After reactivating the protected mode I was back where I started. Is it harmful to have the protected mode disabled? If so what will Mozilla do to correct this very unattractive issue? I will use Chrome until it is solved.

this happens when something like security software is sandboxing/interfering with the process used for flash protected mode. unfortunately those are both external factors, so mozilla can't do anything about it.

for more information about flash protected mode please see the following blog entry & in case you're having further issues please contact adobe's support...

http://blogs.adobe.com/asset/2012/06/inside-flash-player-protected-mode-for-firefox.html

Thanks madperson. But why does it only affect Firefox if it is an external factor?

because adobe has only developed/enabled this protected mode for its flash plugin for firefox. ie uses a different version of the plugin altogether (activeX) & google has an agreement with adobe that the plugin is deployed directly in the chrome browser.

what kind of security related programs are running on your pc? personally i could only replicate those slowdowns with old versions of f-secure or trusteer rapport - but the issues seem to be coming up time & time again...

AVG Internet Security 2012 is as far as I know my only protection.

Which are the risks I take if I use Firefox with disabled protected mode?

Is it only the measured speed that is low or does it also affect the speed of loading pages aso.?

flash protected mode doesn't make any difference to the security of firefox itself, but only for content run by the flash plugin. it adds an additional layer of security for flash & adobe only recommends disabling it as a last resort. the slowdowns you were observing should only occur in flash content too - so for example general page load times or downloading a big file with firefox should be unaffected & will run with the full speed that is available on your connection.

for testing purposes i've tried to install avg 2013 on my machine & played around with a few of its settings but i couldn't reproduce any slowdowns with flash myself - so the cause of the slowdowns might also lie somewhere else...

as stated before, if you'd like to troubleshoot the issue further it would be better to contact adobe's support, since they will have a better understanding of the internals of flash protected mode & therefore may know what else might be at the root of the problem you were seeing.

http://forums.adobe.com/thread/1018071

Thank you again madperson. The slowdown must then be a combination of the flash protected mode and that other possible cause as it disappears when the protected mode is disabled. I also have a laptop that shows exactly the same behavior as my desktop. I will, however, take your advice and contact Adobe Support. Thanks again!