I'm only concerned here with PC/Windows browsers. It seems like the goalposts are changing. Here's my take on testing for the future:

Use:

IE 6 - like it or loathe it - we're stuck with it.
Opera - getting there - stick with it expecially for accessibility and mobile apps.
Firebird - getting better - especially as it's going to replace Mozilla in the browser context.

Forget:

Netscape - any version - not being developed
IE 5.5 and below - being repidly eclipsed. - See browser stats at www.w3schools.com
Mozilla - virtually redundant - see the new Firebird takes.

I KNOW there's Linux and Mac - at this stage I'm just talking about PC/Windows. And I'm talking future - not what only exists today.

What does anyone else think?