Have been trying out the deer park alphas for firefox of late. One reason is that firefox has always been a little sluggish on my laptop, especially when swapping between applications, (though fine on my PC at work). I’ve put this down to the slower speed of my laptop harddisk. So far so good, seems a lot quicker, and not that many problems considering it is not even a beta release.

info on the new and planned improvements to firefox for your consumption:
Firefox wiki
Mozilla 2 wiki

The Burning edge shows the latest bug fixes and improvements on a daily basis
blog post about gecko 1.9