Let's see
FirefoxOS has backing from Alcatel, ZTE, Deutsche Telekom, Etisalat, Smart, Sprint, Telecom Italia, Telefnica and Telenor, and Qualcomm. Tizen has Samsung, Intel, NTT DoCoMo,Vodafone and France Telecom backing it. Ubuntu for Phone has ... who exactly? They aren't saying yet. Maybe after MWC. And not shipping before 2014.
As for Google being worried about Samsung and Tizen, get real. Samsung already supports Windows Phone (#5 or #6 worldwide in 2012) and BadaOS (#4 in 2012). But Samsung's Android business is larger than #4....#N together. Considerably so. Tizen isn't shipping yet. Not a concern.