601200 - After changing layout.css.devPixelsPerPx to N and zooming, viewport is too small by a factor of N

Status: RESOLVED WORKSFORME

(Core :: Layout, defect)

Description

[Daniel Holbert [:dholbert]]

STEPS TO REPRODUCE:
 1. Load URL ( http://ftp.mozilla.org/README ) (or probably any page)
 2. In a separate tab, visit about:config
 3. Set layout.css.devPixelsPerPx to 2
 4. Return to the tab with README
 5. Zoom in or out (with Ctrl,+/- or  Ctrl,mousewheel)

ACTUAL RESULTS:
 Content snaps to a smaller viewport, 1/2 the size of the actual usable area.

NOTE: If you set layout.css.devPixelsPerPx to 3 or 4 in step 3, then you end up with a viewport 1/3 or 1/4 of the usable area.

NOTE: If you reload the page, everything becomes fixed.

Comment 1

[Daniel Holbert [:dholbert]]

Attachment: screenshot with layout.css.devPixelsPerPx = 2

Comment 2

[Daniel Holbert [:dholbert]]

Attachment: screenshot with layout.css.devPixelsPerPx = 0.5

(In reply to comment #0)
> NOTE: If you set layout.css.devPixelsPerPx to 3 or 4 in step 3, then you end up
> with a viewport 1/3 or 1/4 of the usable area.

This happens in the reverse direction, too.  If you set the pref to "0.5", you end up with a viewport that's twice as wide as your window.
(This is easier to see if you load something like http://www.mozilla.com/en-US/ , since that URL has more content and is supposed to be horizontally centered.)

Comment 3

[Daniel Holbert [:dholbert]]

This is WORKSFORME these days.

Comment 4

[Daniel Holbert [:dholbert]]

(tested 100.0a1 (2022-03-14) (64-bit) and didn't hit any issues.)