They are barred from naturalisation, legally barred from owning property, and although Lebanon hands out and renews hundreds of thousands of work permits every year to people from Asia, Africa and other Arab countries, only a handful have been given to Palestinians.
All of that also means that they’re not entitled to any social service such as healthcare or education.
And another thing I’ve recently learned about, Lebanese authorities constructed a concrete wall with watch towers around the Ain al-Hilweh refugee camp, the largest Palestinian refugee camp in Lebanon.
Edit: I also forgot to add that, even if they get work permits, some jobs are simply off-limits to them.