I'd just like to mention that https://gimmebar.com allows you to save text snippets in a similar manner, in addition to pretty much any other media type, and doesn't require you to use Facebook for login.
Disclaimer: We (Fictive Kin) built Gimme Bar, so there's quite a bit of bias in my previous statement.
There's a few things you can learn from QuoteRed that makes me want to use them to save text snippets:
1. Their UI is very simple. Upon landing on their site I saw examples right away of how people are using it and started thinking about how I would use this. I got it immediately.
2. Sign up was very easy. One click, done. No need to register for email/pw combo. This can be a negative for some but for me it's a plus.
3. Their getting started flow is brilliant. With clearly defined steps and arrows pointing out exactly what I should do, setting up was very easy. Open up bookmarks bar, dragging and dropping the bookmarklet, etc. I didn't have to worry, I was in good hands.
4. This third point is probably most important. They started me off with an example. Getting to use the product was part of the getting started flow, and when I closed the site I already have a quote in my account. There are no more barriers to entry, I already know how to use their product.
Building a great product is one thing, but that product is not useful there is a huge learning curve. Spend some time crafting your getting started flow, it is very, very important.
Our onboarding for Gimme Bar has gone through a few revisions, and we're never really satisfied with it. We basically hinge everything on the video, hoping that people will grok it from there, which is of course not optimal.
We've done a bit of work doing some more in-depth onboarding flows for some of our other applications (e.g. https://donenotdone.com and https://teuxdeux.com/), and we might revisit how it's done for Gimme Bar at some point soon as well.
Have you considered Mozilla Persona? https://voo.st is pretty successfully using Facebook and Persona together for auth, at least the last I heard from them.
You should be able to get it integrated in an hour or so, and I'd be happy to double-check your code (or submit a pull request myself) if you'd like.
Thanks! I really like what you've done with QuoteRed; it's refreshingly simple and straightforward. I save a ton of quotes/articles all the time, and you've got an interface that lends itself very nicely to this problem.
Disclaimer: We (Fictive Kin) built Gimme Bar, so there's quite a bit of bias in my previous statement.