You didn't say that the "mechanic" at Firestone used a micrometer, which is the only way to know for sure if your rotors are out of spec. Even if they are, I would just drive the car until a rotor gets warped and then change the rotors and pads together. One of my front rotors has been out of spec for over a year (I have a mic), and hopefully everything will be fine until it's time to change the pads.

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1982 300D, black w/ palomino leather, 203K
2001 E320, champagne, 105K (Mom's)
1999 Dodge Dakota, squeaky & battered, 142K