Not sure I'm doing this right

So, I’ve recently started trying to import my own channels. The site says you can use the bookmarklet on any channel or playlist, however, I’m running into issues with both.

On channels, when I try to use the bookmarklet it separates the videos of the channel into weird individual channels and adds videos NOT from the channel I’m trying to scan. For example, I’ll open up PBS’s YT channel and click on the bookmarklet, it’ll then give me like 6 channels separated into like “11k views” or “15k views” and “PBS Learning” even though all the videos are uploaded by PBS’s YT channel. And then as I scroll down I’ll find videos from random other channels, some I’m subscribed to and some I’m not.

When I try to use the bookmarklet on a playlist, it just fully doesn’t work and only gives me error messages and says it can’t scan the playlist or that the bookmarklet isn’t working.

Is this maybe only functional on certain browsers? I’m using Firefox as my browser. I’m just a bit confused and would like to figure out how I can use this correctly.