Okay, I then researched better, and first of all the function I want is called auto‑scrolling
Already knowing what the name of what you want is helps you by a long shot, so I just duckduckwent
For future reference, and for the odd person like me who may want the same feature in the future, it's something within the programs one is using, not the OS.
Apparently, in Windows all the programs have the auto‑scrolling enabled by default, but it is not so in Linux, where one has to set it manually for each program.
tab, enable Use autoscrolling
, it's not possible to chose an option, but there is an extension for it (https://addons.opera.com/en/extensions/details/autoscroll/?display=en
In LibreOffice Tools
, and under Mouse
change Mouse middle button
from "Paste Clipboard" to "Automatic scrolling"
this isn’t possible within the browser. Searching on the net there are just frustrated people who want to disable it, so you won’t find much help there. I found however this extension that will help, designed especially for Linux and Mac, that apparently has the same problem: https://chrome.google.com/webstore/detail/autoscroll/occjjkgifpmdgodlplnacmkejpdionan?utm_source=chrome-app-launcher-info-dialog
I don't use any other program where I may want to use it, so I'll just leave this one here.
Marked as [SOLVED]
20151220 Edit: added Chrome as I now use also this browser.