QUOTE (abu aufa @ Apr 14 2009, 06:55 PM)

What add-on did you think ?

No idea which one but try disabling them all (not removing) and test, if it fixes it enable them one by one.
If 3.x is the reason, try uninstalling then installing a previous version and test again.
I tested my copy of FF 3.0.8 (non beta) and it still loads fine for me.
<edit>
I've seen a few posts in google about trying this:
1. Try clearing your cookies and your cache
2. Type about:config into the URL bar, list of configuration settings for Firefox
3. Locate the setting for 'network.automatic-ntlm-auth.trusted-uris'
4. Set the value of names of the servers to use NTLM with.
5. Locate the setting for 'network.negotiate-auth.trusted-uris'
6. Set the value of names of the servers to use NTLM with.
7. network.automatic-ntlm-auth.allow-proxies = True
8. Restart Firefox - Test URL to again
<edit2>
seems another user had similar issues with a different site but no resolution:
http://support.mozilla.com/tiki-view_forum...9&forumId=1