I know we do not normally give technical tips on this blog, but we have had a couple of calls from clients today, who have upgraded to Firefox V4, and are having some issues. As these issues were easily solved, I thought I would share the solution. The issue has arisen that when trying to access some websites (most common seems to be webmail systems). This results in an error: “Remote XUL. this page uses an unsupported technology that is no longer available by default in Firefox” Fixing this issue is pretty straightforward, and just involves installing an add-on and making a minor configuration change. The add-on can be found via the link below: https://addons.mozilla.org/en-us/firefox/addon/remote-xul-manager/ Once the add-on is installed, you simply need to white list the domain you are trying to access: Orange Firefox button (top Left) -> Web Developer -> Remote XUL Manager Add the domain you are trying to access to the white list, restart Firefox & you should be good to go again. In future if the issue arises again, you will just need to the add additional domains to the white list.