The spinner of the focused tab spins faster than the spinners of background tabs. Tested on latest Windows nightly.

Just discovered that this only seems to happen in the Compact light and dark themes, not the default. Sorry. Subject updated.

We are missing the SVG variants for these. .tab-throbber[busy][progress] on compacttheme.css has: list-style-image: url("chrome://browser/skin/compacttheme/loading-inverted@2x.png"); http://searchfox.org/mozilla-central/rev/f668d2b2c1413452d536210b3ea2999eb81824f3/browser/themes/shared/compacttheme.inc.css#304-310

So the APNG is rotating and our CSS animation is rotating it too, which is why it's moving too fast.

Comment on attachment 8853554 [details] Bug 1352199 - Invert the SVG loading throbber for selected tabs on compact themes. https://reviewboard.mozilla.org/r/125618/#review128224 ::: browser/themes/shared/tabbrowser/loading.svg:17 (Diff revision 1) > - <path fill="#0077ff" fill-opacity=".15" d="M8,0A8,8,0,0,0,0,8a8,8,0,0,0,8,8,8,8,0,0,0,8-8A8,8,0,0,0,8,0ZM8,13A5,5,0,0,1,3,8,5,5,0,0,1,8,3a5,5,0,0,1,5,5A5,5,0,0,1,8,13Z"/> > - <path mask="url(#myMask)" fill="#0090ff" d="M8,3a5,5,0,0,1,5,5h0a1.5,1.5,0,0,0,3,0h0a8,8,0,1,0-.8,3.5l-2.7-1.3A5,5,0,1,1,8,3Z"/> > + <path fill="context-fill" fill-opacity=".15" d="M8,0A8,8,0,0,0,0,8a8,8,0,0,0,8,8,8,8,0,0,0,8-8A8,8,0,0,0,8,0ZM8,13A5,5,0,0,1,3,8,5,5,0,0,1,8,3a5,5,0,0,1,5,5A5,5,0,0,1,8,13Z"/> > + <path mask="url(#myMask)" fill="context-fill" d="M8,3a5,5,0,0,1,5,5h0a1.5,1.5,0,0,0,3,0h0a8,8,0,1,0-.8,3.5l-2.7-1.3A5,5,0,1,1,8,3Z"/> I wasn't sure how to use context-fill here since we would be replacing two colors, though using #fff for the compact themes and #07f for all other places didn't seem much different than what are shipping today.

Comment on attachment 8853554 [details] Bug 1352199 - Invert the SVG loading throbber for selected tabs on compact themes. https://reviewboard.mozilla.org/r/125618/#review128260

Pushed by jwein@mozilla.com: https://hg.mozilla.org/integration/autoland/rev/2e86b8405b5f Invert the SVG loading throbber for selected tabs on compact themes. r=dao