SinhalaKey Firefox extension will help the firefox user to typing sinhalese letters in Firefox. In the current version, only support for SINGRISH (Type sinhala words using English letters as the same sinhala sound comes when read english letters) mode sinhala typing. In future version it'll support other key board layouts.
(Have a small bugs to fixed> When typing "RAYANNA")
http://risingofsilversurfer.blogspot.com/2008/01/sinhalakey-extension-release.html for further informations.
This add-on is not compatible with your version of Firefox because of the following: