Created attachment 8727345 [details] 2016-03-07 12h05_58.mp4 User Agent Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:47.0) Gecko/20100101 Firefox/47.0 Build ID 20160306030215 [Affected versions]: Nightly 47.0a1, Aurora 46.0a2, Release 44.0.2 [Affected platforms]: Tested on Windows 7, Mac OS 10.6, Mac OS 10.11, Windows 10. [Steps to reproduce]: 1. Open Firefox and navigate to a website. 2. Click on the star button to bookmark it. 3. Click on the star button again. 4. Click on the arrow down next to the Folder: item. [Expected result]: 4. "Edit this Bookmark" changes it's width. Sometimes "Edit this Bookmark" flickers and slightly changes it's position, overlaping the bookmarks in the Bookmarks toolbar. [Actual result]: 4. "Edit this Bookmark" shouldn't change it's width. "Edit this Bookmark" shouldn't flicker or change it's position (when clicking the down arrow next to Tags:, "Edit this Bookmark" doesn't change it's width). [Regression range]: Will be added as soon as possible. [Additional notes]: Please see the attached video for more details.