Affected versions

• Firefox 89.0
• Firefox 90.0a1

Affected platforms

• macOS 10.15.7
• Windows 10

Steps to reproduce

1. Launch Firefox
2. Access customize mode
3. Drag the download tool to overflow menu and save the changes
4. Open overflow menu and click and drag down over the download tool

Expected result

• The download tool is not opened in the background

Actual result

• The download tool is opened in the background

Regression range

• This doesn't seem to be a regression, as it happens way back on 2018 builds, and in 2017 there was no overflow menu.

Additional notes

• The issue can be seen in the following attachment
• Ubuntu 20.04 doesn't seem to be affected as it will open the panel as soon as it is clicked, without any animation.