Typically, you have to jump in with both feet if you want to shape web browser features -- you have to use early (read: buggy) releases and leap into the developer community. But what if you're happy with a stable version and just want to offer a bit of constructive criticism? Mozilla will soon have you covered. It's launching Idea Town, an opt-in program that lets you try upcoming features and offer feedback. You won't have to ditch a regular copy of Firefox, and these will only be features that are likely to show up. While this means that you won't get strictly experimental features (think Chrome's flags), it should put more of the development process in your hands.

http://www.engadget.com/2015/07/27/firefox-idea-town/