1956982 - Use a theme variable for tab drag preview background color

Status: NEW

(Firefox :: Tabbed Browser, enhancement)

Description

[Shane Hughes [:aminomancer]]

When dragging a tab, a thumbnail of the tab content is displayed near the mouse cursor. The thumbnail is drawn on a canvas with a white background, which is visible until the thumbnail loads in, and remains visible if there are problems generating or rendering the thumbnail for whatever reason, disrupting the dark mode experience with a bright white block.

I had a script for customizing this, but it can no longer work as the method now uses private fields. But we might as well just make this color themed so it doesn't need to be customized. My script replaced white with getComputedStyle(this).getPropertyValue("--background-color-canvas"), but it seems we can just use Canvas directly for a very simple patch.