The biggest feature that I really hope takes off will be Mozilla Persona, which is will bring the ability to replace all the Login with Facebook and OpenID and remembering a million passwords with a system that allows you to have multiple managed identities with your choice of identity provider.
In many ways BrowserID is an evolution from OpenID, but as it gets built-in to the browser, it should bring an easier adoption curve with it. This can’t happen soon enough, with more and more major sites being cracked and the user data being strewn across the web.
The visual refresh of the browser (see mockups: Mozilla: shorlander: Australis Design Specs for Linux) is going to be great. My favorite part of this is the non-active tabs having low-volume to their appearance. This gives a much nicer feel and the impression that they are truly in the background; your active tab is what everything below it is about.
That will be improved over time as other features of the browser enhance that contextual choice.
GCLI — the Graphics Command Line
This is a developer tool, which allows you to easily access developer tools and commands so that you can try things out while developing on the web platform. It should allow for things like color manipulation, screenshot creation (great for documentation), and other tasks. Documentation at MDN: Tools: GCLI, which leads me to the final thing about Mozilla I’m really looking forward to:
MDN Kuma Switch
This isn’t really in the browser itself, but it’s just as important: the Mozilla Developer Network (MDN) is moving to a different platform, which will allow it to boldly go where no wiki has gone before. I use MDN a lot for learning about the browser and the web, and I’ve even made some minor edits to it before. But the current (soon-to-be-old) platform has what I consider a clunky interface for editing articles, and it’s likely it’s deterred some people from contributing.
The new MDN is based on the same codebase as the awesome Mozilla Support (SUMO), which means that further progress can be shared between both sites.
Really, some great work is afoot. I look forward to seeing what’s next.