Mozilla has shipped Firefox 56 Beta and Developer Edition yesterday. Check out our Firefox 56 compatibility notes to get prepared for the final version coming late September. There are only a few changes because people are working so hard on Project Quantum that delivers significant performance improvements to Firefox 57 shipping in November.
Meanwhile, Firefox 55 shipped this Tuesday is being rolled out gradually. Given many changes made in the latest release, there might be unexpected regressions we haven’t discovered yet. Please do let us know via Twitter or whatever if you encountered any broken site!