Those modern, 1-pixel wide, scrollbars that only expand when you manage to hover over them are a pox on usability. And I say this as someone with a mouse with scrollwheel.
They make it hard to see the size of a document and as you said: operating the scrollbar is fiddly. You can't just grab it. First you have to make it expand, then you have to move the mouse again to grab it, but don't move the mouse too much or the scrollbar will shrink again!
This is on both Linux and Windows. I have no idea what it is like on OSX.
Even worse. On MacOS the scrollbars are invisible by default, and only appear while you scroll, plus a second or so after stopping.
So to grab a scrollbar in MacOS you first have to scroll the document to make the scrollbar appear. Then you have under two seconds to move the pointer on top of the narrow scrollbar so it expands allowing you to grab it before it disappears again.
There is, and I'm pretty sure if you connect a mouse instead of a trackpad it enables by default. It took me a while to workout why I was seeing scrollbars again and how to disable it when I got a mouse.
I've recently installed https://addons.mozilla.org/en-US/firefox/addon/scroll_anywhe... in middle+right click mode, and now miss it everywhere I don't have it (Reader Mode, PDFs, etc.). Unfortunately development looks a bit inactive, and there's no option for locking scrolling into vertical-only if you begin a scroll by dragging vertically.
They make it hard to see the size of a document and as you said: operating the scrollbar is fiddly. You can't just grab it. First you have to make it expand, then you have to move the mouse again to grab it, but don't move the mouse too much or the scrollbar will shrink again!
This is on both Linux and Windows. I have no idea what it is like on OSX.