Here's a detailed article on this topic by CNBC:
cnbc .com/2019/06/18/the-difference-between-bitcoin-and-facebooks-libra.html
In my view, the biggest difference between Facebook's Libra and the Bitcoin is that while Libra is a Stablecoin, Bitcoin is not!
Libra is Mark's coin. He could take it anytime he want.
Not only for Mark, but also for some other founding members. Mark Zuckerberg or Facebook can't fully control the Libra since there are still some founding member of Libra which is targeted by the Facebook that it could reach more than 100 founding members.
And also did you know that Libra is
open-source?
Which the Libra project is open for public. I want to see more upcoming updates on Libra, and also there could be more founding members will be added? Especially how big those companies are coming for Libra.

And counting.....
Facebook says it hopes to reach 100 founding members before the official Libra launch and its open to anyone that meets the requirements, including direct competitors like Google or Twitter.