We recently ran numbers on our user base (like about 3 weeks ago), and found that 10.10, 10.9 and 10.6 all had greater than 10% share of our Mac user base. 10.6 was still close to 19%.
Gonna be some unhappy people when the hammer comes down, and in fairness to Mozilla, the hammer's going to be Apple screwing around with Xcode to prevent 10.6 compatibility. But when that's the last OS that ran legacy PowerPC applications, ran on any Intel Mac and wasn't infected with the iOS herpes, can you blame people for sticking with what works? These numbers are still roughly comparable with 10.6 usage over a year ago.
Which reminds me that I'm reacquiring numbers for our state of the user base. Watch for that soon™.