The mount is stead firm on the window, that arm holding the mirror is firm.

If you hold the mirror to adjust it, the mirror frame will move a few millimeters in each direction until you apply more force and you can turn the whole thing left or right etc. It holds in any positions, but there's some give.

Anyone knows how to tighten that up?

TIA!

 

I tried to do it at first and rearview mirror ended up in my hand... yeah, fell off of the spot where it was mounted.
Underneath I found where the bracket was bit loose (bent loose) and figured that previous owner must have hit it to come off or whatever. Anyhow, tried to bent bracket piece back to tighten it a bit and mounted it back, but there is still a very small play when I am adjusting the mirror. I do not think there is a way to make it 100% tight and solid, these rearview mirrors are just that kind that does not want to get cooperate :/
Good luck

 

Figured it out.

I merely touched it a bit on the mount and it slid right off.

So I removed the grey plastic cover in the head liner by the mirror and unplugged it. (there's a little clip to push on below to remove the plug).

You just need to use a screwdriver and kinda gently bend each metal bracket slightly inward, you probably didn't bend them enough, but it's only about a millimeter max... coz it won't fit otherwise.

Then you force slide it back on. It's hard as a rock right now on mine, finger crossed.

Thanks for feedback.

 

That's it - I used screwdriver as well, much much improved - but I think in mine there is still somewhat of a very very minor play (perhaps 1mm) or less