Ok, I solved it myself as well.
The permissions problem was on my /var/lib/php5 directory. That was preventing session info from being stored. So when I'd log in, I'd get redirected to an "Auth" controlled page, but since there was no session info, cake tries to redirect again to the login page. The loop should stop here, but it apparently doesn't.... Keeps on redirecting, redirecting, etc until Firefox craps out.