Which one are you referring to? I just saw another post about this one that I just installed, which had been removed from the extensions store in Firefox but can still be downloaded from their GitHub repo. I just installed it on my android Firefox.
Edit: sorry, didn’t see that your post was a link. This seems to be the same one but on GitHub
I just started using both recently and it’s great. For the fzf file search, there’s even some extension that can show a preview pane of text files and even images!