Greasy Fork

Doesn't work if the highlight area is larger than the screen size, i.e. any scrolling is required.

Interesting bug, thanks! It seems to not just be any amount of scrolling though, I've selected regions twice as tall as my screen and still get the button. I'm not sure what it is exactly that breaks it, but I wanna look into it sometime.

Just published v3 which should fix this for most sites (I tested before/after on a news site). The problem was a geometry oversight. Thanks for reporting and waiting patiently.

By the way, I don't get the same UI as you do since I'm the script author, but if you have the ability to edit your review from level "bad: does not work" to "ok: works but has bugs", that'd be appreciated since that's objectively speaking the correct evaluation. It's not like this script doesn't/didn't work at all to begin with, you just found an edgecase, so this paints an excessively negative picture for readers. Thanks.

Edit: or if you have a button to mark the issue as resolved/fixed, even better of course! Or maybe the greasyfork devs expect you to even change the status to "good" now, I honestly don't know since I haven't reported issues on other scripts myself yet.