Firefox for Android has been regularly receiving major feature updates over the last couple of months, the latest one being version 66.0 which introduced a new capability preventing websites from automatically playing audio, among others. After this summer, though, the mobile web browser won't be receiving any new feature updates as part of Mozilla's efforts to shift its development resources to a new replacement for Firefox on Android called Fenix.
Mozilla appears to be working in earnest on the new web browser for Android devices, and on September 3 the legacy Firefox will be deprecated when its version 68.1 enters the Extended Support Release (ESR) channel. That means Firefox for Android will only receive security or stability fixes with no new feature updates afterward.
Until then, the timeline for the legacy browser's major updates will still proceed as planned, with major features set for release on May 14 (version 67.0) and July 9 (version 68.0), respectively. It is, perhaps, worth noting that the July 9 release will mark the final feature update for Firefox on Android.
The deprecation of Firefox on Android is set to continue over the succeeding months until Fenix is ready for practical use. However, there's currently no word on when Mozilla plans to release Fenix to the public.