The limitation from Actionscript is on the External Interface. The following browsers/OSes should be supported

IE 5.0 and later, Windows

Netscape 8.0 and later, Windows, Macintosh

Mozilla 1.7.5 and later, Windows, Macintosh

Firefox 1.0 and later, Windows, Macintosh

Safari 1.3 and later, Macintosh

External Interface is not the only way to communicate between Actionscript and Javascript but it is the most reliable. I believe that if the Javascript will reliably support the table above then this project will be labeled a success.