Netscape 6, which was released in 2000 and based on the Mozilla Suite (now SeaMonkey) recommended 64MB of RAM. The Mozilla Suite was the basis of the Phoenix project (later renamed to Firefox) and they shared the same technological underpinnings: Gecko engine, SpiderMonkey JS engine, XUL interface, XPCOM, etc. Phoenix/Firefox was about using the Mozilla technology to deliver just a browser, independent of the suite, with aim of being lighter weight. So while Firefox didn't exist yet its heavier predecessor did.