First add to /etc/environment
(needs sudo)
GTK_OVERLAY_SCROLLING=0
This will make the scroll bars always visible (thank God)
Then we make them thicker, by editing the local user config
nano "$HOME/.config/gtk-3.0/gtk.css"
The file probably does not exist yet, you can adjust the code below to your liking
/* Scrollbar width fixes */
scrollbar.vertical slider,
scrollbar.slider.vertical
{
min-width: 0.9em;
}
scrollbar.horizontal slider,
scrollbar.slider.horizontal
{
min-height: 0.9em;
}
/* Steppers */
* {
-GtkScrollbar-has-backward-stepper: 1;
-GtkScrollbar-has-forward-stepper: 1;
}
scrollbar button {
min-width: 0.9em;
min-height: 0.9em;
}
scrollbar.vertical button.down {
-gtk-icon-source: -gtk-icontheme("pan-down-symbolic");
}
scrollbar.vertical button.up {
-gtk-icon-source: -gtk-icontheme("pan-up-symbolic");
}
scrollbar.horizontal button.down {
-gtk-icon-source: -gtk-icontheme("pan-end-symbolic");
}
scrollbar.horizontal button.up {
-gtk-icon-source: -gtk-icontheme("pan-start-symbolic");
}
undershoot.top, undershoot.right, undershoot.bottom, undershoot.left {
background-image: none;
}
Open Firefox and go to about:config
(accept the risk).
Change widget.non-native-theme.scrollbar.size.override
to the size you want (I used 20
).