Mozilla does not have the negative motivations to enact user-unfriendly and/or privacy compromising features on purpose nor for profit. They have a lot more goodwill stocked-up (not infinite, though) than Google when it comes to the users' interests, as well. Lastly, Mozilla is the traditional underdog.

For these reasons and I'm sure many more, it should not be surprising that the geek-, security-, and privacy-oriented HN crowd has more positive assumptions about Mozilla than Google.