how do bugs happen in browser games ?

( is this a question enough for you d )

Bugs happen in everything. From programming myself, you can't design a perfect system or game, especially not the first time. A bug is basicly and error in the code/script. Sometimes script is conflicting with other code and sometimes it is a small mistake and simple fix, other times it is harder to find. Everything has bugs, game development and more people playing the game helps to uncover bugs that weren't seen as proofreading code already written is pretty tough to just know that's going to mess up or conflict.