Internet Explorer is currently at version 9, and version 10 is supposed to be officially released some time this year. But most people are not using IE9—most Web users that use Microsoft’s browser are still using a less stable, insecure, slow version of IE (either IE8 or something older).
In May 2012, according to at least one statistics website, Google Chrome (all versions combined) became the most popular browser in the world (compared to IE, all versions combined). Chrome was first released in 2008, and has a number of advantages over old browsers like IE8.
Firefox is the most open browser, and is the one with the most add-ons and developer tools (it is a particular favourite amongst web developers). Behind the scenes a new Social API developed by Mozilla promises to deeply integrate the browser with social media services. This could make new extensions with more powerful social media functionality possible.