Try to start Firefox in Safe mode. This mode disables all extensions, user customizations, hardware acceleration, etc. temporarily for diagnostic and troubleshooting. If Firefox works fine in Safe Mode, then this is likely an add-on issue. Restart Firefox in normal mode, then type "About:addons" (without the quotes) in the address bar. Disable your extensions one by one, restarting Firefox between each one, until you find the trouble maker. Once you do, you can disable that add-on and report the issue to that add-on's developer.

A few other basic trouble shooting things you can try is this: Run all Windows Updates, install all needed service packs, etc.

Update your graphics driver (Firefox uses your graphics card for some rendering, and an out of date graphics card driver can cause problems. https://support.mozilla.org/en-US/kb/how-do-i-upgrade-my-graphics-drivers.

Update all your plugins (Flash, Java, etc.): http://www.mozilla.org/plugincheck/.

Download and Install MalwareBytes Anti-Malware, run a full Scan. http://www.malwarebytes.org/. This helps check that there are no viruses on your computer causing issues. You can uninstall this program after you clean off any infections.

Your above posted system details show multiple Java Console extensions.
You can uninstall and remove Java Console extensions, you do not need them to run Java applets.

See:

• http://kb.mozillazine.org/Java#Multiple_Java_Console_extensions

Thanks for the hints, but I can not see it helps.

I have all the Microsoft updates installed, Java and Flash too. I do not use any custom toolbars. I had Ad-block add-on with just few entries which I now blocked. I had no custom plugins, apart of Skype, VLC and Picasa. I had Java console installed which I have now removed

I have 100mbps line with an effective wireless connection of some 17mbps due to lack of n

I removed 3.6.26, restarted it and installed FF 12. The slowness persists.

On some 'clean' pages i.e. cnn.com it does not differ between safe and unsafe mode and I get them in some 9 sec On my swedish page like svd.se I get it in 20-30 sec in a safe mode, while in std mode it can be up to 90 sec. Aftonbaladet.se is even worse: 20 sec in safe mode, 3-5 minutes in std mode.

I have uninstalled 12, restarted and reinstalled 3.6.28 and everything gets back to fairly normal.

//Henryk

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

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

See "Basic Troubleshooting: Make a new profile":

• https://support.mozilla.org/kb/Basic+Troubleshooting#w_8-make-a-new-profile

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

See:

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

OK, haven't done it yet. Just thinking that I frequently use three other laptops (two Think-Pads and yet another Vaio) with exactly the same security set-up (ZA & Awast) and no one of these has ever posed a similar problem when moving from FF 3 upwards.

//Henryk