As written, no, it requires WebExtensions (the manifest.json file is a tipoff).
The basic idea is that it manipulates cookies, though, so it should be possible to write an old-style add-on that does the same thing for TenFourFox. It wouldn't be a direct 1:1 translation but this is not a very complex extension, so it shouldn't be a massive amount of work to port it.
Hey polluks! If you want to easily toggle between the modern and classic interfaces, just add the following to YouTube links:
&disable_polymer=0 uses the modern interface.
&disable_polymer=1 uses the classic interface.
Use a ? instead of & if your YouTube link has no ? parameter. I hope this helps!