As usual with legal stuff, the answer really seems to depends on the nature of was posted, and the employment contract that is in place.
Not really. Per your link, employees are protected in a very narrow subset of cases - where what they are doing on social media is 100% protected labour activity. But firing employees arbitrarily for social media posts (outside of those narrow protections) is completely fine. That's completely backwards from how it works in most of the developed world, where the burden of proof is on the employer who must show that the firing was for a permitted cause, rather than the employee having to show that they were fired for a non-permitted cause.