I have just finished playing a game called "Quest on Dangerous Adventure". It carries Armor Games Quest. I found that the game become lagging after I play till mid-game. I thought it was because the graphics become more complicated. But then at the moment I finished my last quest on the game, the game speed return to normal immediately. I don't know if this is a coincident or what, but I feel that I better put the case here to let the developer notice the issue.
If you continuously play a game, it can always have some performance issues due to heavy use of the Flash Player and your computer. As is the case with this game, which is known. But the fact that the game's running speed returned to normal once you finished all the Quests could be worth mentioning and looking into perhaps, so I will callout @Tasselfoot on this one. Let's see if he can shed some light on this, ok @cytsunny? =)