If I must use Facebook (obviously it's better not to have one), am I better off using it through the Tor browser or through Firefox without Tor?"trommler"
1) Your IP address
2) Your User-Agent, OS, configuration
3) Your Unique ID (by cookies etc)
4) Information you submit there (email, name, who is your friends, photos & so on)
Tor hides only 1)
Tor Browser Bundle also hides 2) and likely 3), but you better don't rely on it.
Better solution is to use Virtual Environment Installation, such as Tails or Whonix. It hides 2) and 3) for sure.
But the main problem is still 4). This is where most of the people fail, and this is how Silk Road was seized