Mozilla has been working on its almost completely rewritten Firefox for Android app for about a year already. At the moment, the open-source project is receiving finishing touches so it can enter the stable release channel in spring. The company has now communicated that the browser won't get full add-on support at launch and will only work with about 100 recommended extensions.
Once the new version of Firefox hits stable, we understand that it will only migrate some add-ons that are part of Mozilla's recommended extensions program from older versions. Other add-ons won't work at launch — the company says that "at this time, we don’t have details on enabling support for extensions not part of the Recommended Extensions program in the new Firefox for Android." However, Mozilla also states it "would like to expand our support to other add-ons," so those will likely come at some point.
The recommended extensions selection consists of high-profile add-ons like Privacy Badger, NoScript, Facebook Container, LastPass, HTTPS Everywhere, and more than 90 others that cover a wide range of use cases. It should thus be a good start and a decent selection for most people.
Additionally, Mozilla states that it will deprecate Firefox Preview Nightly from the Play Store, encouraging users of this unstable version to move to Firefox Preview, where they can continue testing new cutting-edge features ahead of the stable launch. The feature set currently available in Firefox Preview will be migrated to the Firefox for Android Beta during the week of February 17.
If you want access to uBlock Origin (the only add-on the pre-release version supports currently) before the new browser hits the stable channel, you should switch to Firefox Preview in the near future. You can download it over on APK Mirror or from the Play Store. Should you fancy a more stable version of the new app sans extensions, you can switch to the Firefox Beta next week (APK Mirror).