If you say what the site is and give the URL fronm the location bar others will be able to test it.

Please post the exact erorr message.Firefox 10 uses a different User Agent String than Firfox 9, and it is a known issue that some sites have an issue with the particular string. (If so you may need to contact e-mail the site and ask them to fix it - also let us know please if this is suspected )

Other possible problems could be that javascript is not turned on

• use Tools -> Options -> General
• see Javascript

Or that scripts are being blocked by some security or add-blocking software you are using.

That issue can be caused by corrupted cookies.

• https://support.mozilla.org/kb/Cannot+log+in+to+websites

Also make sure that you do not block the cookies from that site.

• http://kb.mozillazine.org/Cookies

Clear the cache and the cookies from sites that cause problems.

"Clear the Cache":

• Tools > Options > Advanced > Network > Offline Storage (Cache): "Clear Now"

"Remove Cookies" from sites causing problems:

• Tools > Options > Privacy > Cookies: "Show Cookies"