Well, I uninstalled the Greasemonkey program from my computer, but someday I'll try morat's new script, but for now, for those reading this who find all this coding talk intimidating, I can report the following method works for me on Daily Mail's site to stop the sticky video player from dropping down and auto playing in articles. Works on other sites, too.
In your Firefox browser, try installing the YesScript add-on. It is an easy click on, click off javascript blocker. That's all it does, no other settings to sort through. It creates a click-on, click off javascript blacklist. When you visit a domain that you've blocked javascript on, the icon in the toolbar turns black. Click the icon and the javascript gets unblocked and the icon clears. Refresh the page to get the scripts working again. It blocks javascript on all pages of the domain, not specific URLs. You click on any web page address of the domain to get the domain blocked. Easy.
If you have the dailymail.co.uk domain blocked using YesScript, here's what happens (by the way, I am describing this using FF's privacy browser on Windows 10, not yet received the Creators 10 update): the home page will not show any looped preview clips from videos, only a still image, usually. Everything else seems to appear and work okay. I like those looped previews, so that's a loss. The page loads much faster though.
In an article, the video player shows just a gray screen, no looped preview or still, and the player remains in place, does not shrink and drop to the lower right and does not play automatically. The video and sound WILL play by just clicking on the player. The article always contains still images from the video so you know what will be on it.
The main problem with YesScript and Daily Mail is that it blocks the Comments from appearing at the bottom of the article. The Comments section appears, but it says 0 comments. If you like reading the comments, or are registered to post them, you would have to unclick the YesScript icon and refresh the page to get the javascript elements working again, then all appears and works normally.
YesScript will also stop pages on other sites that have an annoying autorefresh (like Drudge Report) and back button disablers. On Drudge Report, some of the photos won't appear if javascript is blocked, so I just open up my Edge browser for a few seconds to see what they are (set to Drudge as the home page), then go back to FF.
So, I can confirm that the YesScript add-on will stop the sticky video player, but there are some drawbacks, but it is an easy solution for some. I also have it installed on a Vista operating system laptop and have used it for years. Read more about the add-on here. I have no connection to it:
https://addons.mozilla.org/en-US/firefo ... yesscript/