I haven't found FB to affect my self-esteem. I have a reasonably good knowledge of myself and people in general. I think that gives me a pretty good understanding of FB dynamics. FB is what you make it. Like 1914sierra I use FB to keep in touch with distant friends and family and to interact with them. I have a healthy skepticism of FB itself though.
I was just reading about a psychological experiment that FB conducted or allowed to be conducted on users back in 2012. The owners of FB say that consent to such research is in the TOS and conditions that users agree to when joining FB. I find that troubling.