They believe Jesus was a prophet, but not divine. I’ve heard it said that Mary is mentioned more in the Koran than the bible, can’t say that I know if that is true.
I'm no theologian. And I'm a Protestant, so I don't see Mary quite the way Catholics do. But I find it very odd that Muslims would care at all about the mother of a prophet. What's the point? Now, if Jesus is more than a prophet, if He is the only begotten Son of God, then His mother would indeed be a significant figure. But Muslims seem to downgrade Jesus but care very much about His mother. I don't get it.