I have a Linux machine and windows machine and suddenly Facebook chat no longer works. I don't see the contacts and if someone initiates a chat the chat box comes up at bottom but it's blank.

Using Firefox in Linux Mint 17.1. (forget what flavour, think it's Mate)

I tried clearing cookies, cache etc... Worked fine yesterday... Anyone know what would cause this?

Are you sure that FB chat still works? I found this article dated from last year. I know nothing about FB so I have no idea if it's relevant or not.
Facebook gives up on desktop apps: Facebook Messenger for Firefox will also shut down on March 3

WHOOPS!! Just found this:
Is this what you're using?
jdk

I'm just using the Facebook site itself. Though I hate that they got rid of XMPP as I used to use pidgen.

Though it randomly started to work again, so that was weird... Not sure how long it's going to last though.

It looks like Facebook wants you to use messanger.com. Have you tried that one?
jdk

Never knew about that one, I guess it's worth checking out.

Weird, started doing it again... but that messenger site works, so guess I'll just start using that. I know the mobile app version of that is full of spyware, should I have to worry about something web based like that? Like does it have the ability to check stuff on my computer like personal info? Then again if it can they could easily do the same with the main FB page...

I eventually want to setup a XMPP server or something as I only have a couple friends I actually chat regularly with so it would not be a huge deal to switch. I had more people I chatted with in MSN but lost contact with them when MS pulled the plug.

Yeah, happens here too, problem is probably on their end. The messenger app has not failed, so just use that. Avast does not detect it as spyware.