Passwords are typically sent to the server and hashed there. I'm a bit hazy right now on the implications of client-side hashing, but it would likely present some security problems.
Edit: at the least, it would allow an attacker to use a leaked password database to log in to the sites, sidestepping the whole hashing thing.
There are protocols that send a hashed or encrypted password instead of plaintext, but they're more complex than just hashing. Iirc they involve a challenge-and-response method.
Imgur users on ‘new’ once ran an experiment for a day where they upvoted basically anything — in practice, oddest and weirdest stuff bubbled up. I've never seen such entertaining feed before or after.