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

Start Firefox in Diagnose Firefox issues using Troubleshoot Mode to check if one of the extensions or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance/Themes).

• Don't make any changes on the Safe mode start window.
• https://support.mozilla.org/kb/Safe+Mode

See also:

• https://support.mozilla.org/kb/reset-firefox-easily-fix-most-problems

Hi, thanks for advise. However I tried both answers separately, but they didn't work for me

- I made my firewall to ask for permission for Firefox to continue - I started Firefox in Safe mode withour making any selections.

I also checked my firewall log and it seems that Firefox has always been allowed.

Any other ideas?

hello jko63, how are you measuring the connection speed - with a flash based test like speedtest.net? then it is possibly an issue with the latest flash update & adobe's introduction of the protected mode - try disabling the protected mode or downgrade to a prior flash version to see if this is making a difference...

http://forums.adobe.com/thread/1018071?tstart=0

Adobe Flash plugin has crashed - Prevent it from happening again