If you want firebug for Safari, you just have to go to the apple extensions and search for Firebug
Why do you want to use Firebug if Safari already comes with great Developer tools? :)
As Matt said, you can enable them from the preferences menu.
Here you will find an overview, summarized, of the Safari's Web inspector, and how to use it:
The Safari built in dev tool is great. I have to admit that Firebug on Firefox is my long time favorite, but I think that the Safari tool do a great job too!
I work a lot with CSS panel and it's too slow in Safari Web Inspector. Apple knows about this problem and promise to fix this bug with freezes, except this thing web tools is much more powerful and convenient than firebug in mozilla, so waiting for fix.
Firebug lite plugin in Safari extensions didn't work (it's made by slicefactory, I don't think it's offical). btw, #2 works for me!
Other than the builtin developer tools, there is none that i know of. You might, however, be able to use Firebug Lite.
Source: Stackoverflow.com