Could JQuery and similar tools be built into the browser install?

Question

After reading another question about JQuery and CDN's, is it feasible for tools like JQuery to "come with" the browser, thus reducing/eliminating the need for the first download from a CDN, or from your own host server.

JQuery files specifically are pretty small, so you could easily have a number (all?) of the different versions as part of a browser install. Now fair enough, this would increase install footprint, download time for the browser itself.

Then sites could check "local" first, before CDN (which then caches), before finally defaulting to downloading from the website server itself.

If this is feasible, has it been done, and if not, why hasn't it be done?