Just like their popular browser, it appears that Mozilla will impose a similar speedy release cycle on their Firefox OS. According to a Tech Radar article, Mozilla's Manager of Release Management, Alex Keybol, "promised significant quarterly updates to the Firefox mobile OS" - with security updates coming every six-weeks.
Mozilla's goal is to outdo its competitors in one area specifically - emerging markets. Firefox OS is scheduled to be released in 16 countries this year, though it will not be coming to the UK or US until 2014. This is not surprising since those markets are already saturated by Android and iOS. Mozilla will likely only move into the US and UK once Firefox OS gains traction the developing world - the reverse strategy of Google and Apple.