Upload photos from MacBook Air library to Facebook

a) Either Photos.app > File > Export (original or edited version) to some Finder folder and choose that in the Facebook export dialog.

b) Or Photos.app > Settings... > Use as System Photo Library. Then you can choose Photos in the Facebook export dialog's side panel:

Berwman wrote:

"Use as Photo Systems Library" is grayed out and doesn't allow me to select it. After I attempt to upload a picture, "it" still asks me to upload a picture and doesn't acknowledge that I just uploaded it.

"Export" is not an option offered to me; only "Import (copy photos).

"Use System Photo Library" button is grayed when it is set as such. Yes, that is a bit misleading and confusing.

So you should be able to select Media > Photos (scroll all the way to the bottom in the sidebar) as in the screenshot I attached in my previous reply (I used Facebook via Safari but might try another browser like Firefox).

Photos.app > File > Export should be available when you have selected desired image(s) to be exported.