If you aren't already using Google Chrome as your Internet browser, I highly recommend it. I do use Firefox in the event that Chrome doesn't work for a specific website or task, but I do find Chrome to be superior most of the time. Recently I've encountered a few extensions to Chrome that may prove to be useful in the classroom.
A Cleaner You Tube - I know of several websites that can be used to clean up specific You Tube video and remove the undesirable comments, etc. This extension is a little different though. It cleans up all of You Tube. That means you could probably safely search for a specific video in front of your class and not worry about the Miller Light ad popping up on the side. Yes, that happened to me last year. I don't think I would use it for my own browsing, but for the times you might need to look for something while you've got a class in the room, this could be handy. Simply install the extension and then go visit You Tube. You will see the difference immediately. The websites I mentioned earlier for cleaning up specific You Tube videos are ViewPure and SafeShare TV. I will still use those sites, but they work a bit differently than the A Cleaner You Tube extension. If you install the extension and then decide you don't like it or would like to disable it temporarily, here are the directions for doing that.
Timer Tab - This is an extension you can add to Chrome or you can access it by simply going to timer-tab.com. If you install the extension, you can access it offline. You can use it as a timer, alarm, or stopwatch. The countdown is visible in the top tab, so you don't need to stay on that webpage while the timer is working. If you install the extension, you can access it by simply opening a new tab and clicking on the Timer Tab icon.
If you know of other Chrome extensions that are useful for the classroom, please feel free to leave information about them in the comments of this post.