I just started working on an extension recently with no experience and have found it to be pleasantly unchallenging. If you are familiar with web development al

I just started working on an extension recently with no experience and have found it to be pleasantly unchallenging. If you are familiar with web development already, it's actually a pretty easy transition. Primarily you have the option of injecting some JS into every page, and also running a page in the background. So you just need to design your extension to work that way. Then you have access to some extension-specific APIs for stuff like the little icon in the toolbar or reading cookies. I think if you already know web dev, you probably don't need a specific resource to figure it out - just dive right into it and look up which parts of API you need for certain things. If you don't already know web dev, perhaps it would be better to learn that first and then look at extensions.