Sometimes the updater gets confused, so in this case, your best option is to go to www.getfirefox.com, and download and install Firefox 11 from there. You can just do it over your current install and non of your personal data will be touched.

Thank you for you really prompt reply. Problem solved. Version 11 now up & running :-))

Arundel, just so you know there will probably update notices later this week for the Firefox 12.0 (unless you check manually) as Firefox is officially released on April 24.

took you a while to finally update to 11.0 and now 12.0 is soon to be out.