Building FirefoxPortable from source

Hey,

I am curious about building FirefoxPortable from source.

Since I want to use a customized version of Firefox, I want to build it from source.
Now, I've successfully build a version, but it turned out bigger than the offered one. (The patches are small and few, they should not take up significant space.)
I see for example the folder named chrome, which the portable version does not have.
Deleting this makes FF not start.

My question is, what flags do you use when building?
And what do you delete afterwards, etc?

I'm trying to make it as small as possible.

Thanks in advance.