As I said above, Lester Holt of NBC News interviewed Trump, who said, he was going to fire him regardless of any recommendation and basically admitted that the Clinton emails had nothing to do with the decision. Instead, he fired Comey for pursuing the Russian connection: “And in fact, when I decided to just do it, I said to myself, I said, ‘You know, this Russia thing with Trump and Russia is a made-up story,’”
In other words, Trump wanted to stop the investigation of the Russian connection, because Trump decided it was "a made up story," unworthy of investigation.