For Twitter (NYSE:TWTR), much has changed in the last two months.

Back in January, CEO Dick Costolo was widely considered to be on the hotseat. 2014 was a poor year for Twitter shareholders: the stock lost over 40% of its value, and despite shuffling senior management (a new CFO and COO, among others), the company appeared directionless.

But last month, Twitter turned in a report that was better than expected, sending shares higher in the process, and the calls for Costolo's ousting have died down. Twitter's management may have bought itself some time, but it will need to keep performing in the months ahead.

User growth has been anemic
As a public company, Twitter's biggest problem has been its user growth -- more specifically, its lack thereof. Twitter had just 288 million monthly active users last quarter -- far less than Facebook, and even less than Instagram.

Twitter is growing -- as of the end of 2013, it had 241 million active users. But the growth has not been as fast as analysts had anticipated. In October, Twitter shares plunged more than 10% after it reported slowing user growth.

To some extent, the intense focus on user growth has been a byproduct of management's own expectations -- Costolo once identified it as his top priority. With its goal to become the world's public square, Twitter can't afford to be a niche offering.

The cries for Costolo's job reached a fever pitch last fall. CNBC's Jim Cramer predicted that Twitter shares could rally more than 30% if Costolo were replaced; SunTrust's Robert Peck actually sent shares higher in December by forecasting his imminent exit. In contrast, Twitter's founders Evan Williams and Jack Dorsey have publicly supported Costolo, but it may not matter. Unlike Facebook's iconic founder Mark Zuckerberg, all are minority shareholders.

But Twitter's monetization is improving
To the credit of Twitter's management, the company's financials have been improving. In February, Twitter's earnings (an adjusted $0.12 per share) and revenue ($479 million) strongly exceeded analyst estimates ($0.06 and $453 million, respectively), and Twitter announced a key strategic deal with Google that will soon allow tweets to show up in search results.

Twitter is also showing some promise as a product. Meerkat, an upstart broadcasting tool built on top of Twitter, has attracted a great deal of attention in recent weeks, notably at the South by Southwest festival. Unfortunately, Twitter doesn't actually own Meerkat -- it bought a competitor, Periscope, instead -- but it does suggest that there's significant untapped potential in Twitter's platform. Potential that, if channeled properly, could attract new users and heighten engagement.

2015 could be a key year for Twitter's C-suite
Will Costolo be there to unlock it? February's earnings report was undoubtedly strong, and Twitter appears to be moving in the right direction. But it was only one quarter after a string of disappointments. Since its public debut, Twitter has underperformed the broader S&P 500, while Facebook (despite being a larger, more mature company) has completely blown it away.

TWTR Chart

TWTR data by YCharts

It may be premature to call for Costolo's outing at this point, but like SunTrust's Peck, I wouldn't be surprised to see him replaced if the company's user growth remains subdued, or its earnings take a turn for the worse.