FYI the interior mirror in my 2014 is made by Volvo, says so stamped inside, probably intended to fit in some Volvo. Keep in mind this mirror is the one for pre-AP cars. Simpler gear and a different mirror design up there on the windshield. Back then, OE parts were sourced from other manufacturers, seemed the normal thing for Tesla to do for getting cars to market. ... now maybe Tesla makes their own mirror.
I had my mirror apart because I wanted to see if I could mount radar detector display inside.. I could.. but chose not to.
What I did with the interior mirror was rotate it 180 degrees so now it is upside down. Why? It didn't turn all the mirror images 180* as some might think
... but this actually raises up the mirror a few millimeters so you can see more under it. I'm a tall driver, continuously ducking my head down to see road / pedestrians on right side of car.. every millimeter gained under that mirror is several feet of roadway seen under it when glancing in that direction. Also, the upside down mirror shape better accommodates the curvature / shape of the rear window image as seen in the mirror... the top arc of the rear window closely follows the mirror edge arc .. so aesthetics.. it's a better image fill and use of the mirror space. I didn't realize this until after doing the work, just a nice bonus.
What about dimming? I found turning the mirror upside down did not affect the excellent auto-dimming feature.. it still works well. Auto dimming must sense a differential of light hitting the mirror glass versus ambient light level sensed through the windshield. All three mirrors are driven by the auto-dimming decisions of the interior mirror.
Test: the best and strongest (darkest) effect of auto-dimming is at dusk, near sundown.. point the car east allowing the glimmering last rays of sunshine to hit the interior mirror dead-on. All your mirrors should become very darkened within a couple minutes.
Check the "view to ambient" from the forward facing side of the interior mirror, that it has a clear view out the windshield. Mine has a little sensor on it. Obstruction (radar detector in the way?) or window tint film, etc. would affect system judgement for dimming, and maybe cause some degree of "perma-darkening" and bottoming out in darkness with no more room to dim .. so the system would seems less active.
Also, rear window tinting diminishes the effect of auto-dimming. It would dim less because less light is hitting the mirror glass surface. So rear window tint means your outside mirrors also aren't dimming as much as they could, which means you're getting beaned in the eyes from the side mirrors showing headlights behind you whereas the window tint makes center mirror glare more bearable. Removing the rear tint would darken side mirrors more.