Goo-Gone or WD40 would be my first choice. I would be very leary of using Acetone since it is pretty strong and will desolve most plastics, rubber, acrylics and polymers.
To be safe, try using a small amount of GooGone or WD-40 on a small area of the rubber first to see that it does not harm the rubber. If that tests succeeds, then you might want to try to remove a small part of the vent visor glue.
At this point, If it does damage the rubber you may want to see if there is any treatment like Back-To-Black, or Armour-All that might restore the finish. If the rubber is not damaged then you can probably proceed with caution.
If it does damage the rubber, you have a choice to continue and just replace the old vent visor with a new one to hide the damaged rubber, or assume that you will need to replace the rubber.
If you have to use acetone, I would not leave it on very long and assume that if nothing else worked, acetone is your last resort before you buy a new replacement weatherstrip for your back window.
...Rich