The option panel for the Downloads Menu shows above the download icon when it's in the icon grid. The style looks a bit off from the other orientation so let's just have it show up on the left hand side all the time since this is likely to be the most common orientation people see.

Comment on attachment 8909155 [details] Bug 1399935 - use horizontal panel for downloads checkbox panel at all times, https://reviewboard.mozilla.org/r/180732/#review185968 ::: browser/base/content/browser.css:187 (Diff revision 1) > .tabbrowser-tab[tabdrop-samewindow], > .tabbrowser-tabs[movingtab] > .tabbrowser-tab[fadein]:not([selected]) { > transition: transform 200ms var(--animation-easing-function); > } > > -#TabsToolbar[movingtab] > .chromeclass-toolbar-additional, > +#TabsToolbar[movingtab] { As discussed over IRC, these browser.css change are in the wrong changeset and should be removed from here ::: browser/components/customizableui/CustomizeMode.jsm:2375 (Diff revision 1) > - checkbox.removeAttribute("checked"); > - } > - > let offsetX = 0, offsetY = 0; > - let position; > + let panelOnTheLeft = false; > + let buttonIsOnToolbar = false; nit: could just initialize it to button.closest("toolbar") and save a couple lines of code, unless it's expensive, but doesn't look like a problem.

Pushed by gijskruitbosch@gmail.com: https://hg.mozilla.org/integration/autoland/rev/7d2984916128 use horizontal panel for downloads checkbox panel at all times, r=mak

I have reproduced the issue mentioned in comment 0 using an affected Firefox 57.0a1 build (BuildId:20170914220255). I have verified that the issue is not reproducible using Firefox 57.0b7 (Build Id:20171009192146) on Windows 10 64bit, macOS 10.11.6 and Ubuntu 16.04 64bit.