What's changing with the new cache? Well... this new cache is a ground-up totally-from-scratch implementation that has been built with just one thing in mind-- correctness. Besides being functionally correct we aimed at keeping the performance of the cache good. (measured in the relative page-loading time difference between the first and subsequent fetch) Since this is the first cut of the new design we didn't work on any great optimizations as yet and are hoping to address that after we land and are stable enough.
In terms of user-experience after this landing hopefully cached copies should load significantly faster (unless someone has slower disk than the network access) and modulo a few bugs we should be doing the right thing with Reloads/Shift-Reloads etc.
As is with every new design, we need all the help we can from the community to test this out and file bugs (against product-Browser, component-Networking:Cache) and also to be patient as we fix them. A very useful thing on that front would be to have people try out and compare (if they can) builds with and without the new cache (toggled by MOZ_NEW_CACHE-- and dependent on the platform) This will help us track the bugs down faster by identifying if the problem exists in the new cache implementation or in the usage of it-- since we haven't changed much on the usage side as yet.
