Up until a few months ago, I seem to remember all of the images for the game only had to be downloaded after a maintainence update, though these days it seems to have to download each and every image (map part, buildings, etc) each time I log in. I am using Firefox 31 on Win7, but AFIK it doesn't cache using Chrome or firefox in either Win7 or Ubuntu 14.04 (both 64-bit).
my cache settings for flash and the browsers are set to keep the cache, browsing history, etc, and I have the latest (14) flash, though Firefox in Ubuntu uses the old v11 or 12 . whatever the last one was before adobe stupidly dropped support for the growing Linux scene.
It would lower the BB servers load considerably if more stuff was cached locally surely?