My webhost recommended downloading Remote XUL Manager add-on, because I can no longer read my webmail properly on their server. I opened the Remote XUL manager download page and clicked "download", whereupon I was asked to restart Firefox in order to get the component installed, which I did....but when the browser restarted it just returned me to the download page. So nothing seems to have happened. I went back to my webmail box just to check if the add-on had actually installed without my realising it, but no joy there either.