When co-founder Jack Dorsey returned to Twitter earlier this year, he announced that his top priority would be to improve the service\'s user experience. On Thursday, Twitter unveiled the first fruit of that labor: A major redesign aimed at making Twitter faster, simpler, and more intuitive for casual users.The new interface will roll out to all Twitter users over the next few weeks. It\'s also available immediately to those who download Twitter\'s iPhone or Android apps.The revamped Twitter has large \"home,\" \"connect,\" and \"discover\" buttons at the top of the homepage. On the left side of the screen, a smaller box invites users to Tweet, and below that visitors can view trending topics and Twitter\'s \"who to follow\" suggestions. Twitter\'s nickname for the redesign: #LetsFly.The changes carry through to Twitter\'s completely redesigned iOS and Android apps -- an acknowledgement that mobile is becoming the main playing field for social and messaging services like Twitter. More than half of Twitter\'s 100 million active members reach the site through mobile devices, Twitter CEO Dick Costolo said in September.Twitter\'s redesign aims to solve one of the main criticisms leveled at the service: that it\'s bewildering to those who don\'t know its jargon and conventions. Hashtags (#) and @ handles help Twitter\'s power users jam lots of meaning into 140 characters, but they can scare off newbies.\"Twitter should be usable by those who know the shortcuts and those who don\'t,\" Dorsey said Thursday at a press event in San Francisco where the redesign was unveiled.The company also ramped up its expansion of videos and photos, which will now display within the tweets that contain them.The revamp is \"a conceptual redesign of the whole product,\" Costolo said at the launch event. \"We can and have an obligation to reach every person on the planet.\"Asked how Twitter will stand out in a social networking world dominated by Facebook and filled with upstart rivals like Google+, he answered: \"We will offer simplicity in a world of complexity.\"Twitter, which celebrated its fifth birthday this year, significantly revamped its website a year ago in a redesign it dubbed #NewTwitter. Playing off that theme, Costolo fired off a tweet praising Twitter\'s team for its work on #NewNewTwitter.