Mozilla released the rewritten Firefox for Android browser ('Fenix'/'Daylight') earlier this year, which was promptly followed by several updates bringing back features from the older version. Firefox 84 is now rolling out on the Play Store, including more returning features and some performance enhancements.
The main design change in v84 is a new option to view tabs in a grid view, similar to how Chrome (and the old Firefox) organize tabs. The list view is still default, but you can change it by opening the tabs page, tapping the 3-dot menu, and pressing 'Tab settings'.
Mozilla has also updated the Downloads page with an option to delete files without leaving the browser. Finally, Firefox 87 begins the rollout of the WebRender compositing engine to devices with Mali-G GPUs, vastly improving performance in typical web browsing. WebRender was already enabled for most devices with Adreno GPUs, so after this release, the technology should be available to the vast majority of Android phones and tablets.
Firefox 84 is rolling out on the Play Store now, but if you don't want to wait, you can grab the APK right now from APKMirror.