Edit: Thank you for the solution, it covered every single problem that I listed and it works perfectly!.

*For anyone not familiar with using Firefox Developer Tools:
after clicking on F12 and selecting the "Console Tab" you need to then paste the code below into the bottom left of the "Console Tab" then press the Enter key on your keyboard, *do not paste the code at the top right!.
Code below:

document.querySelectorAll("button button").forEach(node => node.remove())

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SingleFileZ & Singlefile are no longer working with the latest update to Waterfox Classic 2021.01.

The layout when saving a videos webpage & all comments on *youtube* are now all over the place.

The youtube comments are now on the far right (which can't be read as they are cut off) & the video icon is all out of place & not actually captured.

I really like this add-on...
*but I have never been able to save a youtube video webpage with all of the videos comments shown as is* yet, while trying to do so using (Waterfox Classic), even with any of the older versions of this add-on & I am unsure why?.

As even when it did work for me on Waterfox Classic, when saving a videos webpage on youtube, it always saved all of the suggested videos (that should of been saved on the right hand side of the webpage) but instead it saved & placed them all underneath all of the comments, it also placed them all on the left hand side of the webpage instead!).
It would also only save a huge video image at the top of the webpage (instead of the small default sized video image).

*[I'm unsure if it makes any difference to how your add-on saves a webpage and its layout, but I do change my Waterfox Classic browsers user agent string to Googlebot 2.1 when I'm browsing or saving webpages on youtube!, as this works better for me on an older PC.]*

If you are able to fix any of the above problems or suggest a way that I can save a webpage on youtube *as is, that would be great.
Thank you.