Having read that some users have had difficulties with Firefox 4, I took the precaution of installing the update on a reserve machine (not the one from which this message is being sent), which runs on Windows XP Home Edition SP3, with broadband access via a USB1 port, and with the NoScript add-on operational. I found: (1) that the program was slow to respond to mouse operations, and did so in a jerky fashion; (2) that it was slow to load websites (far slower than previous versions of Firefox, or indeed any other browser I've ever used); and (3) that the the BBC iPlayer would not play programmes — despite the fact that the BBC states that Firefox 4 is the only version on which the new iPlayer can be operated. I uninstalled version 4.0.1 via Control Panel/Add or Remove Programs, reinstalled version 3.6.12 from an .exe file downloaded last year, and updated it to version 3.6.17. The Navigation Bar layout was still that of version 4.0.1, but I was able to restore it to the previous layout via 'Customise'. Can anyone suggest solutions to the above, please?