[Affected versions]: - 60.3.0esr , 63.0.1, 64.0b6, 65.0a1 (2018-11-04) [Affected platforms]: - Win10, Ubuntu 16.04LTS [Steps to reproduce]: 1. Launch Firefox and maximize the window; 2. Access any webpage, ex: https://www.youtube.com/ 3. Open the DevTools - Storage inspector; 4. Click on the Add Item button; 5. Repeat step 4 a couple of times; [Expected result]: - a new cookie is added to the list; [Actual result]: - the name column keeps expanding with each new click until it reaches its max_set width; [Regression range]: - last good: 2017-05-14 - first bad: 2017-05-15 - issue appeared with the introduction of the Add Element button; [Additional notes]: - attached recording with the issue; - it would make sense to expand to fit the text, but it keep on expanding creating extra empty space that is not needed; - was unable to reproduce on macOS(10.13); - while checking for the regression range(on older versions 2017_2018), on some versions the expand did not happen until multiple items where added to the list and it wasn't gradual;