Hi

That add-on is currently unavailable in Firefox for Android, but may be included in a future update.

Note that you posted with an unsupported older Firefox 68.0 (Fennec) version for Android and not with a current Fenix release. I don't think that extensions for this Fennec release are still available.

I also have tried using the latest Firefox app same thing has happened

It can't be the same thing.

You can install this extension only in the Nightly version. And it's working.

See https://blog.mozilla.org/addons/2020/09/29/expanded-extension-support-in-firefox-for-android-nightly/