@Juanito
Yes, cairo and glib are shared in all cases, as well as some other dynamic deps. I only listed static ones. Of course if you have multiple webkitgtk browsers, then webkit is shared between them.
@Lee
In general, I find the movement to "apps on the web" completely wrong. Javascript is being used for things it has no place in, to the detriment of both developers and users. It is terrible to code in due to many reasons, speaking from experience; badly coded JS hogs cpu like no other, also from experience. Compatibility across browsers is fairly bad, and if one of the big frameworks drops support for the one you use, half the internet breaks.
I also think GL, CL, audio and video do not belong in the browser. Surely integration and games-at-work are nice, but I find that an abuse of the original purpose, sharing information. Games and calculations need native performance, having them shoehorned to the browser just opens up a huge attack surface. The moment WebCL becomes widespread you will see ads that mine bitcoin, throwing users' electricity use up, and that's one of the least malicious uses.
More to the current state, I'm sad of the direction Opera went. Chrome has multiple design choices and default options set such that it collects a lot of data off you, essentially spies on you. It's commonly countered with "you can disable each in the options", but I find it obvious that their being enabled by default conveys quite enough of Google's intent. Further, using Chrome would be like using Facebook: each new update may bring new options, of course set by default to share your information. Whack-a-mole.
Firefox has a bad UI in my opinion, and worse, they keep changing it every few versions. Mozilla has also made a few questionable decisions, such as removing options from the users, and the recent acceptance of DRM.
As the big three are close to unusable, the smaller competitors lack much compatibility (dillo, etc) or features (smaller webkit browsers), what's one to do? Can't exactly keep on using the last workable Opera to eternity.