It's very helpful, when learning how Chrome Extensions work, to download existing extensions, find where on your OS they are stored, then check out their code.
When you compare this with the much more complicated process in Firefox you cannot help but congratulate the Google guys for making this happen. Well done!
No comparison between both. Can I change the URL bar in Google Chrome and add an icon or something to it? No! Can I change the refresh button to something else, add new functionality to the start page? No!
Google Chrome Extensions are just simple HTML5 apps in a small screen, that you access them through clicking an icon. So they can't be complicated. In Firefox it's a different thing, you have access to the whole browser and you can change anything. You can even integrate "DLL (C code)".