MooTools modified built-in objects in future hostile ways. Do you miss that too?

Fuck the future. JavaScript was formed full and feature complete and these newfangled "improvements" are nothing but abominations atop its pure and perfect form.

Polymer is also following the same general approach, and has the advantage of most of it being built into the browser and webstandards.

Yep, I was a huge fan of Mootools back in the day. Took me a long time to switch over to jQuery, and even then it was because I had no other choice.