It used to be a de facto standard in many programs. Since almost no mouse had a scroll wheel, you'd use the space bar or the cursor keys. Spacebar was usually faster, I guess some people still do.

I do this too. The pattern probably dates back to first Unix pagers, or perhaps to the paper era.

Still doing that, also in Thunderbird, to scroll through E-Mails and go to the next one when reaching the end (or pressing "n" or "p" for previous). I even use shift + space to go up again. I thought it was very common. Another alternative, maybe a bit more intuitive is using page up and down buttons.

i love it. my mac doesn't have the home row (don't know if that's how that row of buttons is called) so I use spacebar and shift+spacebar as pgdown and pgup when I am reading

[fn]+[up arrow] = pgup, [fn]+[down arrow] = pgdown, [fn]+[left arrow] = home, [fn]+[right arrow] = end

These are impossible to press with just one hand (or the bottom of my coffee cup in a pinch), though.

I use option + up arrow or option + down arrow sometimes, works the same as spacebar to page up / page down.

In which browser? Doesn't work in Firefox, unfortunately.

Unfortunately I'm using Chrome still.

They're called the navigation keys. Fn + Up/Down (arrow keys) is PgUp/PgDn, and Fn + Left/Right is Home/End. But of course, those keys are on completely opposite sides of the keyboard, so Space is more convenient.

yeah, with spacebar i can use either of my hands while the arrow keys would require me to use both of my hands

I am often annoyed Mac does not have a right Ctrl or a right Fn.

>the home row (don't know if that's how that row of buttons is called)

the "home row" is where your fingers start out if you know how to type by touch, and it come from the days of typewriters instead of keyboards.

on a QWERTY keyboard, the home row is ASDFGHJKL; with your fingers resting on ASDF and JKL;

when they teach you to touch type, they say "put your fingers on the home row" and "home is where your fingers always return to."

"Home row" usually refers to the row where you initially put your fingers when touch typing, to not have to move them much while typing.