Mozilla will be lengthening the beta cycle for Firefox 89 according to the FX Trains website, it will see the release pushed back to June 1 as opposed to May 18 when it was supposed to be released. The alteration to the schedule was noticed by German Firefox blogger Sören Hentzschel who said that the delay has been put in place so Mozilla can have more time to test its new Proton user interface.
With Firefox 89 undergoing a six-week beta cycle, Firefox 90 will also see its nightly cycle length extended to six weeks over the same period before everything returns back to the usual four-week cycle. Firefox 88 will be the final version of Firefox to ship according to the old release calendar on April 20 and subsequent releases will be delayed by two weeks from their original launch dates.
At the time of writing, Firefox 89 is on the Nightly branch. While it’s still being worked on, users can download Firefox Nightly right now to test out the new Proton UI. The most noticeable change with the new interface are the tabs which float in the tab bar rather than appearing to be fixed to the URL bar.
It’ll be interesting to see how Mozilla uses the extra two weeks of beta testing. Users on Reddit have begun complaining about the Proton tab experience as they're upset that it uses up too much space and that there are no visual separators between tabs.