Did your engine start “running real rough” immediately after Firestone replaced the timing belt, or did the rough running begin later? If it was right away, the likelihood is that they screwed-up the belt installation by being one or two teeth “off”. This is something that will damage your engine, so if this situation took place the first time that you drove the car after the timing belt job, then you need to take the car to a competent mechanic (clearly, NOT the Firestone guys) immediately, and then bring the bill for the second job to Firestone for reimbursement.
If the rough running started a day or two later, then it is possible that this is merely a coincidence, and that you really do need to replace coils and plugs. However, the two things that make this scenario very questionable are
- this is not likely on a 2008 vehicle
and - “a catalytic converter cleaning or flush or something like that”.
If they actually told you that they could “clean or flush” your cat converter, I suggest that you never return to this Firestone garage again.
Cleaning or flushing a catalytic converter???
Did they also suggest changing your blinker fluid?
Did they recommend replacing the muffler bearings?