id summary reporter owner description type status priority milestone component version severity resolution keywords cc focuses 33322 Theme Installer: spinner animated GIF and high CPU usage afercia wonderboymusic "In the Theme Installer (Themes > Add New > Preview a Theme), the spinner loading indicator causes the same performance issues noticed for the Customizer spinner a while ago, see https://core.trac.wordpress.org/ticket/31196#comment:14 On modern hardware, with a dedicated GPU and hardware acceleration support, you will barely notice this but on old hardware the CPU usage can easily be over 50% and in the worst case always stuck at 100% since the spinner is always ""spinning"" in the background even when overlaid by the iframe. Looks like modern browser still have issues with animated GIFs especially when some CSS properties (e.g. opacity, box-shadow) are set on the GIF container. I can reproduce high CPU usage using both Chrome and Firefox, they behave differently but the result is the same. Regardless, when the preview iframe loads, the background spinner image should be removed as already done for the Customizer. See also related #33311 for the Thickbox spinner. [[Image(https://cldup.com/NUKm7LaRGM.png)]]" defect (bug) closed normal 4.4 Themes 4.2 normal fixed has-patch ui, javascript