... Reporter
	Description • 8 years ago

User Agent: Mozilla/5.0 (Windows NT 6.3; Win64; x64; rv:47.0) Gecko/20100101 Firefox/47.0
Build ID: 20160131030347

Steps to reproduce:

Set the amount of lines scrolled to 11.
Testing on a new profile shows Firefox scrolls about a line each time whereas IE scrolls the 11 lines.



Expected results:

Firefox should respect custom mouse scroll settings.
Changing the amount of lines scrolled each time in mouse system settings does not correspond to a change in lines scrolled in Firefox.
IE, Edge respect custom scroll settings.

	Masayuki Nakano [:masayuki] (he/him)(JST, +0900)
	Comment 1 • 8 years ago

I cannot reproduce this bug. Don't you test with Synaptics's touchpad? If so, we know that Synaptics's touchpad overrides system settings only when it's being used.

	Masayuki Nakano [:masayuki] (he/him)(JST, +0900)
	Comment 2 • 8 years ago

FYI: When you set both scroll amount (vertical and horizontal) to 3, Firefox makes the scrolling speed multiplied by 2. So, when you set the scroll amount to 11, the scroll amount is changed from 6 to 11. So, multiplied about only by 2.

	... Reporter
	Comment 3 • 8 years ago

I initiated the session with an actual mouse as initiating Firefox using the touchpad results in even worse scrolling.
I think bug 1153156 exacerbated this issue.

Getting the amount of lines scrolled in Firefox to 11 in practice would require changing the system settings to the amount of lines scrolled to ~23. 

However, setting the amount of lines scrolled to 23 results in substantially more amounts of lines scrolled in IE, Explorer and many other applications.

This isn't a good user experience as many other applications scroll way too much.

The amount of lines scrolled should be consistent throughout the system.

	Masayuki Nakano [:masayuki] (he/him)(JST, +0900)
	Comment 4 • 8 years ago

Could you confirm with this testcase with and without e10s?
https://jsfiddle.net/d_toybox/x0e1uj3L/

	... Reporter
	Comment 5 • 8 years ago

Using system scroll settings to 11 vertical lines, the same scrolling behaviour is exhibited between e10s and non-e10s.

One scroll within the first sub-container reaches number 14 at the top with both e10s and non-e10s.
However, IE reaches 19 with one scroll.

Scrolling parity is somewhat evident when changing the setting to one vertical screen at a time with Firefox getting to line 31 at the top of the first sub-container with one scroll and IE to line 29.

Firefox's line scrolling behaviour is the odd one out as most Windows applications scroll identical amounts of lines as IE which should be used as the standard to compare against.

	Michelle Funches - QA
	Comment 6 • 8 years ago

Name 	Firefox
Version 	47.0a1
Build ID 	20160201030241
User Agent 	Mozilla/5.0 (Windows NT 6.3; Win64; x64; rv:47.0) Gecko/20100101 Firefox/47.0
I can reproduce - adding kats@mozilla.com to CC List as may relate to APZ

	Masayuki Nakano [:masayuki] (he/him)(JST, +0900)
	Comment 7 • 8 years ago

(In reply to ... from comment #5)
> Using system scroll settings to 11 vertical lines, the same scrolling
> behaviour is exhibited between e10s and non-e10s.

Good, that's one of the fixes of bug 1153156.

> One scroll within the first sub-container reaches number 14 at the top with
> both e10s and non-e10s.

Good. Although, I guess that your mouse is an expensive mouse which has smoother wheel. With such mouse, it's hard to test only 120 delta (one notch). So, scrolling 14 lines in the first scrollable element is our intentional behavior. Not ignored the prefs as the summary of this bug.

> However, IE reaches 19 with one scroll.

Okay. As far as I've tested, looks like that IE scrolls per line. I.e., depending on the font-size or line-height of the scrollable element (although, I cannot understand what they do exactly...). On the other hand, Google Chrome uses fixed value for any font-size scrollable elements. I.e., major 3 browsers use different approach.

I believe that our current behavior isn't bad at least when line-height: 1.0;.

> Scrolling parity is somewhat evident when changing the setting to one
> vertical screen at a time with Firefox getting to line 31 at the top of the
> first sub-container with one scroll and IE to line 29.

Yeah, our page scroll scrolls page height - one line height because scrolling whole page may make some users confused in some cases.

> Firefox's line scrolling behaviour is the odd one out as most Windows
> applications scroll identical amounts of lines as IE which should be used as
> the standard to compare against.

What's the standard? What scroll amount is the best to you in the first scrollable element the second scrollable element?

	Masayuki Nakano [:masayuki] (he/him)(JST, +0900)
	Comment 8 • 8 years ago

Anyway, this isn't a regression and not related to APZ. Dropping the dependency.

	Masayuki Nakano [:masayuki] (he/him)(JST, +0900)
	Comment 9 • 8 years ago

I tested with Wordpad on Win10, then, one notch of wheel causes exactly 3 lines, i.e., depending on the line height, not font size.

So, it might be better to use line height instead of font size, though.

	... Reporter
	Comment 10 • 8 years ago

Unlike other applications, Firefox's scrolling behaviour seems more resistant and less influenced by the amount of lines scrolled system setting. 

I'm not sure of the exacts mechanics, Firefox just feels off and generally requires a few more scrolls to reach the same point as IE, Explorer, etc with one scroll especially when the amount of lines scrolled setting increases.

Parity with IE would be ideal.