I just installed Read It Later and Screengrab for Firefox and Firebug Lite for Chrome. All three add-ons/extensions are really helpful in my day-to-day management of Wopular.
Recently I've updated the Alexa Sparky add-on for FireFox 3.0, which displays website traffic rankings on the status bar. It's a nice little plugin that not only lets you see how large other sites are, but it also helps improve your rankings a little bit. After updating the add-on, I started noticing some strange behavior while browsing the web.