User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:80.0) Gecko/20100101 Firefox/80.0

Steps to reproduce:

visit website with scroll bars (almost all) - does it on Youtube.com, canvas.umn.edu, vanguard.com, uimn.org, , but NOT gmail, google calendar, cooking.nytimes.com.

Actual results:

the scroll bars are way oversized, like 2-3x the normal size

Expected results:

Scroll bars should be the same on every page and the same size they always have been.

This is the normal scroll bar as I would expect to see it.

Here is another example of the oversized scroll bar

Same for me,
Screen resolution: 3840 x 2160
Windows 10 with custom DPI scaling: 175%
Graphic Card: nVidia 1070 GTX with 442.59 drivers

Setting a component for this issue in order to get the dev team involved.
If you feel it's an incorrect one please feel free to change it to a more appropriate one.

Ryan, thanks for the bug report. I wonder whether this issue is a recent regression or not? I did try to see the result on Firefox 57, it looks like the scrollbar width hasn't been changed. Also to me it looks same scrollbar width on Chrome.

I'm not sure what you mean by "recent" but I've started seeing it in one of the more recent updates, like in the last couple months. There is also a scaling issue in the opposite direction sometimes, especially with checkboxes - they will be so small you can barely click them. I don't use Chrome very much if I can help it, so I don't know what it looks like, sorry.

Yeah, thanks for the info. Though I can't reproduce the issue on my Windows laptop, hopefully someone can reproduce this issue will narrow down the regression range.

Do you have widget.disable-native-theme-for-content set to true in about:config? And if so, what's the display's scale set to in Windows' Display settings?

Nope, it's set to false. Display scale is 250% if it still matters.

Just noticed that on two adjacent google-hosted sites, scrollbars are different sizes. See new images attached.

Big scroll bars

Normal scroll bars

Tried to reproduce this on a 2560 x 1440 monitor witch increased scales but all my browser interface is zoomed in. Looking at the screenshots that's not the case.
Hey Ryan, could you guide me a bit here? How come you set up display case to 250% and the full browser is not zoomed in?

Also, could you please try to install and run and older Firefox version (example FX70-http://archive.mozilla.org/pub/firefox/releases/70.0/win64/en-US/) and see if it can be reproduced there?

So I run a laptop with a 4k panel and a regular 1080p monitor, which I think might be part of the problem. That said, it's never been an issue in the 2+ years I've owned this rig and it only occurs with firefox and only recently. I typically run my firefox scaling at around 100% and it has been fine, but the windows scaling at 250% which is what they recommend.

This is the windows scaling

Also I'm installing the old version to see if that does it too.

Ah, I kind of lack that specific setup. Can you run Mozregression when you have the time and see if you get a pushlog? This method is used to find what introduced this issue since you mention you didn't have this problem until recently.

Hi guys,
I tried installing the mozregression tool and was not able to figure out how to use it or get anything out of it. I also tried installing the old version and was unable to reproduce the issue. I'm not a software developer or tester, and I didn't report this bug to figure out the root cause - just to alert others to it so they could. I've reached the end of my usefulness in this process so I'll hand it over to you guys and either deal with the issue or use another browser. Thanks!

Hey Ryan, if you want I can send you an e-mail with a tutorial on how to use it. Due to the custom setup you have, it is hard for others to try to help you with this further. Let me know if you still wish to work on this or not and I can guide you more thoroughly. Thanks again for your time and I am sorry for this inconvenience.