To replace the AC recirculation filter, locate 2 latches under the glove box, turn both 90-degrees CCW, pull the panel downwards, replace the filter element, push up the panel, turn the latches 90-degrees CW.

To remove the side panel, pry off the door sill trim (no screws or latches), feel for and remove two screws that go horizontally through the right footwell vertical panel into the frame, remove the panel.

I believe at this point you can remove the floor covering (carpet). Obviously the floor mat comes off first. It might not be necessary to fully remove the floor covering depending on what you're doing. You might be able to get away with folding the forward half over the rear half.

To remove the cover of the firewall, remove two nuts that take a 10mm socket along the base of the panel, lift the panel out of place, TAKE ABSOLUTE CARE BECAUSE THERE IS A CABLE DIRECTLY FROM THE BATTERY AND SEVERAL AIRBAG CONNECTIONS!!! Even with the battery disconnected, allow some time for the airbag capacitors to discharge.

At some point you should tell us what you are trying to accomplish.

Sixto
93 300SD