We’ve been encouraging testers and community members to get the Nightly builds of Firefox, the very cutting edge of development. While not always the most stable branch, this is where you can get access to the most recent changes that Mozilla community developers have added to Firefox. Builds are available at nightly.mozilla.org
Marcia and others have made a video about nightly testing, which I’ve added below. We encourage you to get involved. If Nightly builds are just a bit unstable for you, consider running Aurora builds, where we gather up the nightly changes every few weeks, or even our Beta builds of the next Firefox. You can find all of them at www.mozilla.com/firefox/channel/.
Links In Video
More Ways To Test