Browsing the Web from work or with the chance that somebody might catch a passing glance at your screen can sometimes be like playing Russian roulette. You might get caught, you might not. Now if your not one who seeks the thrill of outsmarting the boss you may wish to play it a ‘bit on the safer side with No-NSFW.
The No-NSFW add-on for Firefox will warn you whenever you are about to view a page that may not be suitable for all ages. It is a tiny addition to the browser that lives in your statusbar. You can vote too, when you reach an unrated page to determine if it is safe for work or not.