I don't like the design pattern of hiding the scrollbars. I am not alone in this; I have frequently read articles complaining about it, like this blog post that made it to Hacker News, Reddit posts, or even posts on Microsoft forums.
There are different variations of this pattern. On some cases, the scrollbar is hidden, and it only shows up when hovering the cursors over the area where the scrollbar is supposed to be. On other cases, it's there, but very thin, and it only becomes thicker — although not much nowadays — when you hover over it. I think both cases are bad from a usability and accessibility perspective, and just another example of today's software industry where form triumphs usability.
Personally, I hate the ones that are hidden, as you lose the visual cue of how long the article/content is, and how much is left to scroll.
Anyway, on Firefox on Linux, this can be easily solved on the browser settings. Open the settings window, search for "scrollbar" on the search box, and a checkbox with the text Always show scrollbars should show up. Enable it, and you are back to the good old times!
On Windows 11 it's a bit different. You have to enable it at the OS level. Search for "scroll bar" on the search box of the Windows task bar. The first option it suggests should say Always show scroll bars / System settings. Click on it, and it will open a window titled Accessibility > Visual effects. On it there should be a checkbox with the text Always show scrollbars — you might have noticed they are inconsistent with the spelling of "scrollbar". Enable this option to get back to sanity.
Happy scrolling!