Once you have acquired permanent residency status, that doesn't mean job separation (or, say, divorce) will have any material effect on it.
In this case it very well might. When the employer is the sponsor of the green card and the employee is terminated the employer can and usually does withdraw sponsorship of the green card. At that time the employee can apply for their own or seek a different kind of visa but failure to do so would trigger deportation status.
If I get fired or resign from them do they have the right to revoke my green card and send me back to my home country?
Sponsoring a green card for employment is VERY expensive which is why employers that terminate employees or the employee resigns, end the sponsorship. While the employer cannot revoke the card (only INS can do that) they can withdraw sponsorship which would no longer make you eligible and you would need another sponsor or path to stay legally.
You should consult an immigration attorney ASAP to find out how your termination will affect your green card status.
"That's just my opinion, then again I might be wrong." Dennis Miller