Your attorney could send a cease and desist letter, but I'm not sure what else you can do until his rantings cause you actual harm (ie you lose a job because of his rantings and are told that is the reason; you are arrested on false pretenses based on something he says).

People who know you won't believe it, and people who don't know you probably don't care. I'd ask everyone to stop telling you about it. The more everyone who cares about you ignores his BS, the faster it will stop.

If you really fear for your life or that he could cause serious harm then report him to FB at the very least or go to the cops or get a C&D letter.

Otherwise ignore his FB and tell anyone else to not tell you what this man is saying about you.

It sounds like he likes to drunk post, then? (shrug)

Unless he is communicating clear threats, or it’s libelous, you got nothing. And even then, it’s extraordinarily rare to sue, etcetera.

Look at the plus side. If this twit does carry out anything IRL, at least you’ll have a good amount of witnesses.

Think hard before you do anything that might crank him up even more. Right now, he's just a loud drunk and what he's says doesn't matter if you don't read it. He clearly friended your ex so you'd hear what he's writing - he's desperate to engage you, he's begging for your attention, he's picking a fight. Don't take the bait. The last thing he wants is for you to ignore him. If you engage him, even with a cease and desist letter, you are stirring a pot that doesn't need to be stirred.

If he really threatened to kill your husband, that is your legal leverage, not him talking bad about you.

As they say, and as I have always practiced, an aggressive offense in the best defense. I suggest that you go on the offensive, speak to an attorney and see what your options are to confront and eliminate the BM's current paramour's toxic effluent.

First I would block him on FB so that his verbal feces does not get promulgated to your friends and network.

Quit tolerating and avoiding confrontation and destroy this asshole and his wife.

I would.

Have your dh's lawyer send a STRONG worded letter to Mr. FB dude wife's lawyer.
"It seems that your clients husband Mr. FB dude has repeatedly posted on FB that my clients new wife is a xyz. Mr. FB dude also appears to threatening my client and his family. Kindly instruct your clients husband to stop.
Included at the end:

"I have instructed my client that in the event that Mr. FB dude continues saying blah blah blah on fb that WE will file all appropriate actions against him the court will allow" .

Here's the link:

http://mycbs4.com/news/local/gainesville-man-accused-of-stalking-woman-f...

This is a news story that caught my eye. We all looked at the crazy he posted on his FB page about this woman. Sometimes crazy doesn't stop. Sometimes it escalates. But notice how he was ordered not to post anything about her on social media. Maybe he is drunk posting . Maybe is a dangerous crazy person that you need to protect yourself from. Look at the poor girl from The Voice. She was murdered by a complete stranger. If it were me, I would call the non emergency and ask to speak to an officer. Sometimes they will just call the nut job and tell them to knock it off

BM and Aergia does the same thing about me, first time SIL send me screen shots about it and asked my What are you going to do about this?

I laughed and said, nothing, It's their opinion and how they feel, leave them be, I'm not interested in what they have to say about me.

SIL kept on doing it, eventually I started using it, if Aergia wanted something from me and she was super nice, I would simply ignore it or ask her... oh now suddenly I'm not a whoring bitch any more? She had no clue how I knew the things she posted.... I have BM and her whole family blocked and Aergia and all off her friends.... It stopped after a year or 2 , and now and again they do it ....
2 days ago Aergia did it again, BM jumped on the wagon, and a woman I know off but do not know, told them on FB to grow up and stop their shit, I'm not the way they say I am and they are jealous cause I have more class in my little toe then what they would ever have..... Aergia removed her post, but I have the screen shots... she did it to late little cow lol....

Simply tell your X you are not interested and save everything that's send to you, it might help you one day, or you might never use it, then simply ignore it. People who really know you, know this is crap and stories, simply let it go, it's not going to make a better person or worse person off you, they are showing their colors and people know it...

Can you file for slander, libel, or harassment, no.

However, keep screen shots. If it becomes really over the top where he is demeaning your husband and you on a fairly daily basis you can ask the court to remove him from the house while the children are there as his negativity will adversely effect the children. This also supposes he says similar things in front of or to the children

And then post a pdf of the NCO or C&DO in response to any of his BS and file a contempt motion each time he violates.

Lather, rinse, repeat.

Get someone to report them on facebook.  Facebook generally doesn't allow bullying.  SD's grandparents said some nasty stuff on facebook about us.  I didn't really care--neither did DH.  Neither of us have facebook, and we only found out becuase of SD (who reported them).  

What people say about you is more of a reflection on them, than it is on you.  Don't let it bother you too much.  Though if he's threatening you, you might want to get the police involved.  Especially if they have the ability to carry out that threat.