The "contextual strip" is something most people have become familiar with -- for better or worse. In addition to making the interface easier to navigate, the ribbon menu will improve screen real estate -- a bonus for people using Firefox on very small displays. Mozilla has commented on the change, saying that they feel the existing Firefox UI is too dated and cumbersome, and is becoming inconsistent. The latter bit is probably more important than most people realize.
Even if you dislike ribbon menus, they are increasingly common on modern Windows machines, and familiarity is a plus. Not all hope is lost for the naysayers, though. A mere press of the Alt key will return users to the older (current) interface. Mozilla admits that the move is still a proposal at the moment, and user input will be key in making a final decision.