https://browsercheck.qualys.com/ - on a routine basis both at home and at the office.
Installing the tool in your browser is very easy, and the service is free and painless to use. I have been using it to both to determine if my current browser and plugins are up to date, and also to identify plugins that are installed and enabled, but which I don't really need or use (e.g., Silverlight which I often disable for long stretches at a time).
Qualys generates a nice report
like the one above to let you know if everything is up-to-date.