How does one go about customizing the URL for the social media buttons which appear after clicking the 'open button'? For example, I would like the Facebook link to go directly to a specific page.
I'm not sure what is "open" button, but I assume, you are talking about the webplayer application. There are two options to customize interface.
1) Change the webplayer application. You will have to take a look at apps_dev/webplayer
folder. There are webplayer.html and webplayer.css files which describe html buttons behavior. Facebook button can be found there as "fb_button"
2) Create your own app from scratch. You can follow these tutorials:https://www.blend4web.com/en/author/50/1/
"Furnishing a Room" application just has custom html buttons.
Also, is it possible to set the scene to load in low quality setting by default?
1) If you are customizing webplayer, you can change the DEFAULT_QUALITY variable to "LOW" in the webplayer.js
2) For a custom application you need to pass the "quality" param to the app.init
It should look like this: