1422412 - changing page zoom from default 100% causes menu items to 'twitch' when moused over on google.com

Status: RESOLVED DUPLICATE of bug 1399577

(Firefox :: Untriaged, defect)

Description

[Will]

Attachment: pagezoomtwitchmouseover.png

User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:57.0) Gecko/20100101 Firefox/57.0
Build ID: 20171128222554

Steps to reproduce:

using Firefox 57 on Windows 10 v1703 at 200% system scaling, go to google.com and increase or decrease the page zoom so it is not 100%, then click the grid menu located in the top-right corner and hover the cursor over the items. Notice they 'twitch' when moused over. Now, go back to 100% page zoom and try it again and notice they do not twitch when moused over. This bug is especially important because soon Firefox will have a global zoom option like Chrome and lots of people could see twitching during mouse over (I'm certain that grid menu on google.com is not the only website that has this issue)

Comment 1

[Daniel Holbert [:dholbert]]

FWIW, my Win10 ThinkPad won't let me pick 200% scaling (175% is the max that it offers).  But setting that aside:

(In reply to Will from comment #0)
> using Firefox 57 on Windows 10 v1703 at 200% system scaling

Sounds like at 200% system scaling, with no pagezoom, things are fine. Great! :D

> google.com and increase or decrease the page zoom so it is not 100%, then
> click the grid menu located in the top-right corner and hover the cursor
> over the items.  Notice they 'twitch' when moused over.

Right -- so this is just producing an *effective* zoom factor (CSS-pixel-to-device-pixel) that is not whole-number, and that's the root of the problem here.  So, this is the same as bug 1399577 (and is caused by the special behavior discussed in bug 477157).

I see this same issue even at a default 100%-system-scaling level, if I decrease Firefox's page zoom to 90% (press Ctrl- once) or increase it to 170% (press ctrl+ 5 times).