For those sticking to Mozilla's stable channel, following this week's release of Firefox 45 was the public beta of Firefox 46.0.
All of the Firefox 46.0 beta details can be found via the Mozilla.org release notes. Mozilla developers have been trying for a few release cycles now to ship the GTK3-enabled version of the Firefox web-browser; hopefully Firefox 46 will mark the point where they'll be able to stick to keeping it enabled at release time.
The meta bug report tracking Firefox for using GTK3. The remaining items mostly come down to weird UI behavior issues or misplaced elements.