I would like to understand how jQuery event namespacing works across different browsers.
I don't see anything about this on MDN and I would like to know how to namespace events without using jQuery as well (on older IE as well on modern browsers)
jQuery event namespaces are exactly that – jQuery event namespaces.
This feature is unique to jQuery; the DOM doesn't have anything like it.
The point of event namespaces is the ability to remove your event handlers by name only; the DOM APIs don't do that at all.