Twitter managed to eke out an unexpected $0.02 non-GAAP profit in its first quarter as a public company, but its stock fell a dramatic 18 percent in evening trading after the firm reported slowing user growth. In order to combat the new user slump, Twitter appears to be testing a new sign-up process that directs users from the Web to the mobile app. Sequentially, Twitter gained just 9 million monthly active users in the fourth quarter of 2013, but its active user base grew 30 percent year-over-year growth to 241 million. Judging by the graph Twitter provided, user growth sloped off during the period. Sequential growth from Q3 to Q4 in 2013 weighed in at less than 4 percent, compared to over 10 percent growth from Q3 to Q4 in 2012.