What are these fuzzy window guide things?

Hi FABO:

I'm getting ready to dive in to my weatherstripping, window sweeps etc. and now I'm looking at these hairy looking things wondering what they are, what is their function and where to go to find replacements.

I haven't started taking the door apart yet to take a better look as I have a feeling things connected to the glass could get 'complicated'

As always, your input is appreciated.