Rated 5 out of 5 stars
This is a very useful extension from one of the most overworked developers in the world!
A few things that could be improved:
1) It only seems to show the current year. At least, the PageUp/PageDown keys and the mouse scrollwheel don't change years.
2) If I'm in month view in August, switch to year view then back to month view, the current month is now January instead of August.
3) The current day is highlighted in the current month and in the previous month. For example, today is 7 August and in year view this day and 7 July are both highlighted.
That's all forgivable because the initial version of this extension is just for the benefit of "showing how to do it" and other developers can improve it.