Firefox 3.6 has fallen over 1% in the past 30 days to under 5%. It will fall below IE7 in the next 30 days. In a few months, [with the adoption of FF 10 ES] 3.6 will be ancient history.
[Update] Added some text to make my point explicit.
[Update] Added some text to make my point explicit.
Also, Firefox 3.6 was released about 2 years ago. The extended support period for Firefox 10 will only be "about a year". That sounds reasonable given the market share decline rate of 3.6 you quoted.