Taken Straight from the Release Notes:
FireFox 1.5 has better accessibility including support for DHTML accessibility and assistive technologies such as the Window-Eyes 5.5 beta screen reader for Microsoft Windows. Screen readers read aloud all available information in applications and documents or show the information on a Braille display, enabling blind and visually impaired users to use equivalent software functionality as their sighted peers.
This is a good worthwhile development.