Mozilla Firefox is based on Gecko, the rendering engine that came out of Netscape years ago. There is also Mozilla Suite (called Seamonkey, I think) that is an all in one product -- browser, email, web design editor, kitchen sink. And yes, they all come from the open sourcing of netscape. Flock and some others also use the gecko engine making them also "based" on netscape originally, though they've come a long way since then.
I'm no expert on this, so take all the above as nothing but talk around the water cooler.
A