[Note]: - Logged based on Bug 1241587 Comment 5 [Affected versions]: - Firefox 48.0a1 (2016-04-12) [Affected platforms]: - Windows 7 x 64, Ubuntu 14.04 x86, Mac OS x 10.11 [Steps to reproduce]: 1. Launch Firefox. 2. From about:config, enable the devtools.responsive.html.enabled pref. 3. Open RDM. 4. Click on a scrollbar from viewport and without releasing the click, move the cursor outside the viewport window and release the click button. 5. Move the mouse cursor over the viewport window. [Expected result]: - After step 4, the position of the scrollbar is switched back to it's previous position and the scrollbar is deselected. - At step 5, nothing happens. [Actual result]: - The scrollbar remains selected, and without using the click button, the page is scrolled, depending how the cursor is moved. [Regression range]: This is not a regression since this is a new implementation.