[mnemonik]

When you enter debug mode in SpiderMonkey most (all? I forget) jit'ing and optimizations won't happen; code becomes a lot slower. The new debugging api allows you to debug specific tabs, while the old one would force all of the browser (including the chrome js that handles the browser's UI) to enter debug mode and the whole browser gets slow.

Because Honza is working on porting firebug to the new debugger API, it will get faster, and so will all of firefox when you are using firebug.

IIRC, Honza is not just working on porting from the old api to the new one, but also on top of our remote debugging protocol. This means that we improve the debugging server, and both the native tools and firebug get better. Plus, you'll be able to use firebug on your laptop, connected remotely to firefox on your android phone, or firefox os.