Arrows are here in TB 60 on Windows, irrespective of theme. Check if you have a broken layout by seeing if the arrows appear in safe mode (Help/Restart with Add-ons disabled).

http://kb.mozillazine.org/Toolbar_or_windows_layout_not_working

jelabarre59 said

Just wondering which theme/UI system the Thunderbird 60 Beta is using. In the older versions (including the latest v52.x build) my scrollbars still have top & bottom arrows. In TB Beta v60.x, those arrows are now gone. Would like to put them back where they belong, and don't want to have to hunt down some ugly, unmaintained theme to do it.

The missing scrollbar arrows tells me you may have a GTK2 theme in use on your Linux distro instead of a GTK3 theme.

The official Firefox builds for Linux from Mozilla since 46.0+ have required both GTK 3.4 (three.four) or later and also a GTK3 Theme in use for Firefox or Thunderbird 60.0 to be themed. If a GTK2 theme is in use then it will look unthemed and some glitches like say missing the scroolbar arrows. Some Linux distros may have delayed this change in their Firefox and Thunderbird packages until later versions.

Though it may be possible the scrollbar arrows may be not visible but will work if you click on where they should be in version 60.0.

James said

The official Firefox builds for Linux from Mozilla since 46.0+ have required both GTK 3.4 (three.four) or later and also a GTK3 Theme in use for Firefox or Thunderbird 60.0 to be themed. If a GTK2 theme is in use then it will look unthemed and some glitches like say missing the scroolbar arrows. Some Linux distros may have delayed this change in their Firefox and Thunderbird packages until later versions. Though it may be possible the scrollbar arrows may be not visible but will work if you click on where they should be in version 60.0.

So in other words, I can only theme GTK3 applications OR GTK2, but not both? But yes, the arrows are apparently invisible; clicking in the blank space at the ends of the scrollbar makes the area scroll properly, and the "thumb" does not move into that space. It's workable/functional for now, will just need to clean up the aesthetics later.