For those who live in most modern western countries you'll get a shock when you first come to Vietnam to find that most cafes, hotels and restaurants provide free WIFI (and good speeds).
If you are staying at a hotel that less than 4 or 5 stars you will most likely get some type of fibre Internet connection. Some places wil have better Internet than others.
If you are having trouble connecting to Facebook you can update your DNS settings to use Google: 8.8.8.8. If you are a Windows user check how to edit your dns settings on Windows. If you are using Mac you can check how to edit your dns settings on Mac.
Hope this helps and enjoy your time in Vietnam!
