What I like about Firefox's App Tabs is how narrow they are -- just the width of an icon, plus a little padding. What I don't like about Firefox's App Tabs is how narrow they are...
I use an App Tab for Google+. I'd also be using them for GMail and SEO Content Factory if it weren't for one thing: since they only show the icon, I can't tell without going to the tab whether I've got new stuff to read. With a full-sized tab that displays the title of the page, I can see unread item counts while I'm on another tab.
If you've got pages that you visit often, but which you don't want to put in an App Tab since you need to be able to see the title, one solution is to put them on your bookmarks bar instead. Once you've got them there, right click, select "Properties" from the context menu, delete the entire title, and save.
Only the icon will be displayed on your bookmarks bar. But when you open a tab, the title will be displayed, so you'll be able to see the status information.