Firefox Preview has only received a significant update with version 5.2 with improved tab management and voice search a few days ago, but Mozilla is already working on the next feature-filled update. The unstable Nightly now supports three new add-ons and sees smaller refinements to the three-button overflow menu. The dead-space custom tab bug that's plaguing the current Firefox Preview build is also nowhere to be seen.
The three new extensions in question are the privacy tool Decentraleyes, tracking blocker Privacy Possum, and YouTube High Definition, a simple tool forcing HD on YouTube videos and bringing overall enhancements to the website. Other than that, the overflow menu has seen small improvements. There's now an always-visible Synced tabs shortcut for quick access to sites opened in other Firefox instances, and the Add-ons shortcut has an arrow, indicating that you open another overflow menu when you tap it. To my delight, the Nightly release also got rid of some dead space in custom tabs that's currently plaguing the more stable preview build.
Left: Firefox Preview 5.2. Middle: Firefox Preview Nightly. Right: Fixed custom tabs.
The changes are live in Firefox Nightly, available from the Play Store or APK Mirror.
Updated with the correct Play Store link according to the new, simplified Firefox lineup for Android.