4 days ago, I read a Mozilla employee writing "Seamonkey does not interest anyone inside Mozilla. Who would nowadays use a Netscape-like tool?".
Just one example why Seamonkey is important (for me at least).
So it actually does exactly what you want?!
I can assure you that they do not, because Firefox requires heavy tweaking to run comfortably in 1 gigabyte of RAM.
Seamonkey is real nice though.