Here's from the what's New page on Mozilla:
and the link to the same page:
Firefox 8 Release NotesWhat’s New in Firefox
The latest version of Firefox has the following changes:
Add-ons installed by third party programs are now disabled by default
Added a one-time add-on selection dialog to manage previously installed add-ons
Added Twitter to the search bar for select locales. Additional locale support will be added in the future
Added a preference to load tabs on demand, improving start-up time when windows are restored
Improved performance and memory handling when using <audio> and <video> elements
Added CORS support for cross-domain textures in WebGL
Added support for HTML5 context menus
Added support for insertAdjacentHTML
Improved CSS hyphen support for many languages
Improved WebSocket support
Fixed several stability issues
Fixed several security issues
Please see the complete list of changes in this version. Web and extension developers should also view the curated list of platform changes. You may also be interested in the list of changes in the previous version.