1486134 - the right hand side tab scroll button doesn't switch to 'disabled' state when it's supposed to at 175% DPI

Status: RESOLVED FIXED

(Firefox :: Tabbed Browser, defect, P3)

Description

[Will]

Attachment: tabscrollarrow.png

User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:61.0) Gecko/20100101 Firefox/61.0
Build ID: 20180807170231

Steps to reproduce:

When you have enough tabs open, the tab bar scroll buttons appear. On my machine, when I scroll all the way to the right, the right arrow doesn't switch to the 'unavailable' state like it's supposed to. Strangely, the one on the left hand side doesn't have this problem. See screenshot attached (in the screenshot with the red arrow, I am all the way over to the right and I have clicked the button many times, it just won't switch to the 'unavailable' state like it should). The green arrow is how it's supposed to look.

Just guessing but I think this might have to do with the fact that my Windows 10 system scaling is set to 175%, I've heard that system scalings like this can cause issues like this

Comment 1

[Will]

Attachment: tabscrollbug175percent.png

I found a good way to reproduce the issue: set the Windows 10 system scaling to 175%. Then, make sure the Firefox window is not maximized. Grab the right hand side of the window and adjust the width. As you're adjusting the window width, observe the button flashing between available and unavailable.

Comment 2

[Daniel_A[:daschilean] [Please contact - [e-mail]]]

User Agent:  Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:61.0) Gecko/20100101 Firefox/61.0
Build ID: 20180807170231                  
I manage to reproduce this issue on Windows 10 x64 with Firefox Nightly 63.0a1 (2018-08-28) (64-bit). Please note that this issue is also displayed with the latest Firefox release version 62.0 (64-bit).

Comment 3

[Will]

not sure if this is helpful or not but I found a couple of similar bugs in Chrome (though it's for webpage content, not the GUI)
https://bugs.chromium.org/p/chromium/issues/detail?id=807790
https://bugs.chromium.org/p/chromium/issues/detail?id=818873

Comment 4

[Will]

Apparently 125% system scaling is very common, and when you add up all these different types of fractional scale factors (125%, 175% etc.), this issue is effecting a lot of users

Comment 5

[Will]

From our own data, scroll down to Display Resolution section https://data.firefox.com/dashboard/hardware 1920 x 1080 is about to overtake 1366 x 768 (no one is using 100% system scaling on a 1080 display), so probably a majority of Firefox users are seeing this bug. I'm still seeing it on version 65.0.2, this issue is worthy of some attention

Comment 6

[Dão Gottwald [:dao]]

Bug 1913322 may have fixed this. Will, would you mind testing in Nightly?

Comment 7

[Will]

Just checked and I can no longer repro the problem! Thank you