A strict order is specified with all resources set to "exclusive" (only browser to use the exclusive bit). No concurrency for images but really good for JS, CSS, etc. Ordering is based on priorities from blink.
High-level groupings are created for the resource types and weighted so more-important types get more bandwidth. Within a group all resources are peers, weighted equally (i.e. all scripts download concurrently with a lower weight than css).
No dependencies/grouping. All resources are weighted based on the webkit resource priority (JS/css: 24, font: 16, image: 8). Looks a lot like Chrome's old SPDY implementation but HTTP/2 weights don't work the same way.
No dependencies, everything gets a weight of 16. Probably a side-effect of the architecture with HTTP/2 being implemented deep in the OS with no priority/dependency info.
Chrome and Firefox are the only two I'd say "support" HTTP/2, the others only support the framing (barely)