Bottle holders are on the inside of the doors.

CAUTION
Do not use the bottle holders for containers without caps. The contents may spill when the door is opened or closed.
Cup Holder
Storage CompartmentsMazda 6 Owners Manual: Scheduled Maintenance (U.S.A., Canada, and Puerto Rico)
Follow Schedule 1 if the vehicle is operated mainly where none of the following
conditions (severe driving conditions) apply.
Repeated short-distance driving
Driving in dusty conditions
Driving with extended use of brakes
Driving in areas where salt or other corrosive materials are used
...
Mazda 6 Owners Manual: Power window regulator removal/installation
1. Disconnect the negative battery cable.
2. Remove the front door glass/rear door glass.
3. Remove the front door speaker/rear door speaker.
4. Remove the power window motor.
5. Remove the nuts.
6. Insert hand through the speaker installation hole, rotate the regulator
drum housing in the ...