If you use Google Chrome browser, one of the must have tool is the Google Dictionary. If you find any word you want to explain, double click on it, Google Dictionary will show the explanation as well as a icon for the sound.
I have used Firefox for many years. But recently I found out Chrome is better and faster than Firefox. Best feature I like is the Chrome Sync, which will sync you book marks, browse history, tool bar across multiple computers.
It also better integrate with other Google services. You can install free Web apps including Angry Bird and Plants vs. Zombie.
Update: I have install Chrome for Android on ASUS Transformer (just upgrade to ICS 4.0). I liked it. The best thing is I can get all my bookmarks using Chrome Sync.