The fundamental difference is that Google is a gigantic engineering organization that dedicates enormous resources to security, benefiting Chrome directly and indirectly. Over the years, lots of work has been done to ensure and improve its security at a design and architectural level.

Firefox, as this announcement shows, is just getting around to freeing itself from design decisions which may have made sense over a decade ago when Mozilla had 'software suite' ambitions but we now know are a liability for something with the security demands of a browser.