The black borders on SocialAPI currently were used as a default because other left-sidebars in Firefox end with a 1-pixel black line. However, this color in SocialAPI includes far more lines than a standard sidebar as it surrounds chat windows and even titlebars in chat windows. Those black lines give the interface a heavy, weighted feeling. Lightening the borders to #cccccc grey will help the interface feel lighter.
Created attachment 673424 [details] Mockup: Current state with #000000 lines and goal state with #cccccc
Created attachment 673740 [details] [diff] [review] Patch
This wouldn't block release so I'm not tracking but please nominate the patches for uplift when ready.
Comment on attachment 673740 [details] [diff] [review] Patch [Triage Comment] a=me for 17/18
Does this bug really warrant a "major" severity?
Verified fixed with a quick spotcheck.