What version of Flash are you running? I think I read that the latest bug fix (.265) had reduced performance in Flash games in Firefox for some people. Perhaps it also affects your speed test? You can get the version number down to the last decimal place on Adobe's About page: http://www.adobe.com/software/flash/about/

I have disabled and removed all extensions and plugins. I have un-installed Firefox. I have removed remnant from disk and registry. I have installed Firefox 14.0.1 again. Speedtest.net asked to install the latest Flash. So i did. "You have version 11,3,300,265 installed."

Just tsted with Opera. Speed is as expected 50 Mb/s.

Only with Firefox i lose 40% of bandwith.

The trouble was in the Adobe Flash-plugin. Had to manually edit the flash-config-file, so that the 'protected-mode' gets disabled.

Still: Why is a flash-plugin allowed to cripple not only flash related stuff, but the whole browser??

For now it is fixed. Have to wait for a flash update..:-(

I'm not sure the whole browser is crippled, but Flash is used so pervasively and sometimes invisibly that it can seem that way.

For other readers, here is how you disable the new protected mode in Flash 11.3. See this support article from Adobe under the heading "Last Resort": Adobe Forums: How do I troubleshoot Flash Player's protected mode for Firefox?

To make things even simpler: - - To disable Protected Mode, add the following line to your mms.cfg file located in:

Windows 32bit: C:\windows\system32\macromed\flash

Windows 64bit: C:\windows\syswow64\macromed\flash

ProtectedMode=0

If the mms.cfg file does not exist, create one using any standard text editor (e.g.. notepad) .

My Firefox runs like a charm again.

Thank you very much for the help.