Yes, we reverse engineered Puffin 2.x and implemented a partially featured client in python. We used this client to run map reduce on puffin's servers. You can read about some of the benchmarks we measured here:
The short answer to your question is they run and render all the js/html/css in a server farm (rackspace when we benchmarked it) and send the client a rendered stream of the contents. The paper above gives the benchmarks we measured.
Note: all the above is only relevant to Puffin 2.x. Im not sure how much has been redesigned for 3.x None of the above may be correct for current versions.
http://ix.cs.uoregon.edu/~butler/pubs/acsac12.pdf
The short answer to your question is they run and render all the js/html/css in a server farm (rackspace when we benchmarked it) and send the client a rendered stream of the contents. The paper above gives the benchmarks we measured.
Note: all the above is only relevant to Puffin 2.x. Im not sure how much has been redesigned for 3.x None of the above may be correct for current versions.