It's not (actually) down but 504 Gateway Timeout error to be precise. It just means that one particular server did not receive a timely response from another server that it was accessing while attempting to load the Quora or fill another request by the browser.
In other words, 504 error usually indicates that a different computer, the one that you're trying to access Quora on doesn't control but relies on, isn't communicating with it quickly enough. Give it some time.
I'm generally pretty out-of-touch when it comes to social media/app trends (I finally made an Instagram account this year). What exactly is Quora? It seems like Yahoo answers, but people seem to give it more respect.
In other words, 504 error usually indicates that a different computer, the one that you're trying to access Quora on doesn't control but relies on, isn't communicating with it quickly enough. Give it some time.