Many post described these problems. A solution is upgrade to BD 2011 or later (?). Tried to obtain support in reporting the problem to French support.
No acknoldgement received after 3 days. Not very serious !
The good news is that there is an excellent uninstall tool on the BD site. After running this program and restarting, my Firefox worked like a charm.
This means that I say Good Bye to Bit Defender which has been successfully replaced by Microsoft Security Essential.
Hope this post will not be censored.