When I play for some time disconnects happens quite often, it's irritating especially on events (and when I play on 3 servers it happens almost always after a while, so it's impossible to play simultaneously on them).
To describe it on Firefox screen becames completely black and only the lowest inscriptions (Official website | Recharge | Online support | Forum) are visible, to connect again you need to refresh the game.
On other browser based on Chromium only half of the screen became black (or sometimes even less), but game stops working and you can only refresh and re-connect to it.
A lot of people reported this that their games DCs too, before I thought it's due to my weak connection with internet, but that doesn't seems to be the case.
1st. Depending on your internet connection speed and your computer capabilities. I wouldn't play on 3 server at same time. Do you still have problem when just playing on one server?
2nd. Are these the only browsers you use? I suggest using Internet Explorer to see if that fixes your problem.
3rd. Try downloading the latest version for Flash Player. See if that helps a bit.