It hasn’t been officially announced, but the mirrors don’t lie.
This isn’t beta, this isn’t an RC, it’s the final 1.5 product
Here’s what’s in the new version:
-Error pages now are XHTML pages loaded in the tab/window that the error occured under, rather than new dialog windows.
-New navigation code make the page back/forward navigation much much faster
-New cleaner preferences dialog
-Drag and Drop tab reordering
-Auto update system, without installers
-Canvas in xhtml/js
-New xhtml stuff
The extensions aren’t incompatible per se, they’re simply not labeled explicitly support 1.5, thus they won’t install or work. This is the extension author’s fault more than mozilla’s though.
My 3 extensions work fine though, Goggle Toolbar, Adblock Plus and Web Developer