Since bottoming out last November, Groupon shares have more than quadrupled. The company’s stock closed yesterday near its 52-week high. Its market cap is back above $8 billion, still a far cry from its IPO days, but once again worth more than Nokia. After being written off as a dying business (by me, among others), Groupon is staging one of the year’s more unlikely comebacks.

Though Groupon shares began to rise again before ex-CEO and co-founder Andrew Mason was fired at the end of February, the real rebound didn’t get under way until after he was gone. Under Mason, Groupon shed nearly 80 percent of its value during the first nine months after its 20122 IPO—at the time, the biggest internet IPO since Google. As Mason himself pointed out in his much-shared note following his departure.

“From controversial metrics in our S1 to our material weakness to two quarters of missing our own expectations and a stock price that’s hovering around one quarter of our listing price, the events of the last year and a half speak for themselves,” he said. “As CEO, I am accountable.”