I agree with this firing. Mularkey isn't head coaching material IMO. He will go enrich a staff somewhere as OC though, where he's best served. This is no different than Whisenhunt being fired so early, and MM just learned that what comes around goes around.
Also in spite of the talent there in Tennessee, it won't be the top coveted job due to questions with the QB as well as the seeming impatience of the front office.
Josh McDaniels covets this job, per Ian Rappaport
I seriously doubt that McDaniels wants to suffer through the minefield brought on by an inaccurate QB whose legs are his best asset. He suffered through that in Denver (when he actually won some games with Tebow).
Best job will either be one that has a QB he can develop in place, OR a very high pick that he can bring around. Also he might strongly consider a team if they convince him they're serious about bringing in a FA QB of sufficient quality, since Brees might hit the market and Cousins certainly will.
This offseason is going to be one of the most tumultuous ever in terms of QB turnover and fortunes of many teams will be affected.