Facebook was completely generic. Facebook used to be term for the paperback student profile books that universities produced. Facebook the website started as an electronic version of the paper facebooks.
Yes, Facebook WAS generic. They would have had a difficult time enforcing their brand from the start. Once a brand becomes a household name (which is admittedly a vague metric), the rules are different. See Apple, Windows, Sun, Sharp, Digital.
The standard isn't "household name", but rather "acquired distinctiveness" which in the US is defined under the terms of Section 2(f) of the Trademark Act
Yes, Facebook WAS generic. They would have had a difficult time enforcing their brand from the start. Once a brand becomes a household name (which is admittedly a vague metric), the rules are different. See Apple, Windows, Sun, Sharp, Digital.