[Affected versions]: - latest Nightly 62.0a1 - Beta 61.0b11 [Affected platforms]: - Win 10 x64 - macOS 10.13 - Ubuntu 16.04 x64 [Steps to reproduce]: 1. Launch Firefox. 2. Access any website, e.g. https://youtube.com 3. Enable the Accessibility feature and the "Pick accessible object from the page" button. 4. Click on one of the elements displayed on the page's content (choose an image that has a long value). 5. Resize the width of the Properties panel until some of the links (from `value` or `attributes`) are no longer displayed entirely. 6. Grab the vertical scrollbar and scroll the panel down slowly. - observe the behavior when the horizontal scrollbars appear [Expected result]: - The horizontal scrollbar is fully functional and doesn't flicker [Actual result]: - The horizontal scrollbar flickers and the panel can't be scrolled anymore using the mouse [Regression range]: - It doesn't seem to be a regression, I was able to reproduce this issue on Nightly from 2018-04-05 as well. [Additional notes]: - see the attached screencast - please note that if the Devtools is resized again after step 6, the horizontal scrollbar starts to work properly

(In reply to Ciprian Georgiu, QA [:ciprian_georgiu] from comment #0) > [Regression range]: > - It doesn't seem to be a regression, I was able to reproduce this issue on > Nightly from 2018-04-05 as well. Could you try running mozregression? It could be a regression older than 2018-04-05.

I can repro this on 61.0a1 (2018-04-04) too, the last build that has the `devtools.accessibility.enabled` pref created.

Here's a link to a try build with possible fix for this issue, Ciprian, could you verify if it fixes things for you: https://treeherder.mozilla.org/#/jobs?repo=try&revision=5fcbc7113141958f6ff1ff470123c6a80161dfa1

Unfortunately, it didn't fix the issue on my end, I can sill reproduce the bug on the provided try build. I've tested on Win 10 x64 and macOS 10.13. Please see the following screencast: https://drive.google.com/file/d/1fOALyuhvMBmOWOJXlVAkAXQy5tmboVyK/view?usp=sharing