It's not a problem with flash persay, the game have a serious memory leak problem, so the longer it's kept open, the more problematic it becomes
It also spawns zombies so refreshing/close-reopen don't work as well as it should, you need to hasten the zombie reaps by manually go through the task manager.


That said, having a good PC and connection would significantly improve performance. I have no issues of the sort whatsoever unless I keep the game running for more than 100 fights (note it's measured in fights as keeping it on idle doesn't generate much leakage). Thou in the case of my laptop, the game more or less demand one of the cores, so I'm limited on what other loads I can put on it (my desktop can handle stuff fine)

But in any case, slow loading is almost always internet issue, computer issue manifest in the way of fight delays, fight crashes, glitch jutsu and that sort of thing. And @mys....@gmail.com, it could be your country. When I took a trip to China, the connection was HORRIBLE regardless of if I use VPN. Now, this doesn't mean that your country have slow internet exactly, I can watch video on Chinese sites at full HD fine at the time, it's just a matter of the connection hopping through too many hoops and the country and/or ISP placing filter on things that delays your package because they like to take a peek at it first.