The pages created using the publishing Active Site component ARE Firefox compatible, the publishing tool itself does still require Internet Explorer, however with the move to using TinyMCE in the V5.00 release the WHOLE application is now a lot closer to being cross browser compatible, as the previous DHTML editor was IE specific (TinyMCE is cross browser compatible).
Your concerns over full Firefox compatibility are duly noted, if any developers out there would like to assist in the final changes required for Firefox compatibility please in touch.
Cheers,
Ian.