UPDATE: I never liked the man (though I'm okay with his policies) but this is either pure cowardice (unlikely, I hope) or coarse, solipsistic behavior of the worst sort: Trump didn't bother speaking with Tillerson, simply tweeted his decision to fire him.
The two had their differences, fine; but Tillerson put his personal life on hold, at Trump's request, and served the country tirelessly and well for 14 months. Common decency would demand that Trump fire him personally, and maybe even thank him, but if there's anything we've known about Trump for decades, he is not a man of decency. In fact, he's a disgusting, low class (okay, no class) human being.
It's still better to have him in office, instead of Hillary, but that's not saying much.
UPDATE II: Apparently Tillerson was working against Trump's attempts to undo the Iran deal Obama put together, and in general, was resisting Trump's policies. For that, he did deserve to be fired, so my objection is now down merely to Trump's rudeness, and we already knew he was rude. So, whatever.