The Winter Bash FAQ mentions:
I'm on Stack Overflow (or on one of a few other sites). Where are my hats?
Users on these sites have to choose to opt-in individually. Just click the "Winter Bash" popup at the top and click "I love hats!", and you'll be able to earn hats and see other hat-loving users sporting dashing works of millinery.
I don't see a pop-up (snowflake) on TeX.SE, nor is it listed in the Winter Bash Leaderboard. Are all sites able to participate in Winter Bash 2014? What about per-site metas (as it's currently not available on Meta.SO)?
Related (not duplicate): Where is my snowflake on Stack Overflow?; I tried in both Google Chrome and Mozilla Firefox with no luck, nor am I running any of mentioned extensions/plug-ins.