By Jed Horowitz NEW YORK (Reuters) – Morgan Stanley is further opening the social media door for its brokers by allowing them to post self-authored content on firm-approved Twitter accounts. Morgan Stanley, the worlds largest brokerage firm as measured by its more than 16,000 financial advisers, has until now limited them to tweeting scripted messages it prepared on the economy, general investment themes, wealth management concepts and some lifestyle topics. The company told advisers on Monday that if they take an online training course that can be completed in about 20 minutes and have at least 15 followers – a pittance by the standards of Twitter, where Justin Bieber has 52.6 million followers – they can create their own 140-character messages and retweet content from others. Morgan Stanley is the first of the big U.S. brokerages – the others are Wells Fargo Cos Wells Fargo Advisors, Bank of Americas Merrill Lynch and UBS AGs UBS Wealth Management Americas – to allow such leeway, said Valentina Chtchedrine, executive director for digital marketing strategy.