Although Firefox 37.0 was released on Tuesday, the number of automatic updates is limited so that Mozilla can watch for any major problems among early adopters. If you're in a hurry, you can download the full installer instead of waiting for the upgrade (scroll down to your language):

https://www.mozilla.org/firefox/all/

Note: Do not uninstall. The full installer will find your existing settings.

hmm That's why, I wondered why the Firefox download page(https://www.mozilla.org/en-US/firefox/new/) is saying "Looks like you’re using an older version of Firefox. "

Actually the automatic update was 25% on Tuesday and automatic update was planned to be disabled on Wednesday but due to a problem crasher(s) mostly on Windows the updates was disabled completely on Wednesday until Fx 37.0.1 is released.