Created attachment 8848945 [details] Current contents of tab-selected-start.svg While triaging and bumping into bug 921673 I just happened to look in: https://dxr.mozilla.org/mozilla-central/source/obj-x86_64-pc-linux-gnu/browser/themes/linux/tab-selected-start.svg If I understand the CSS gradient syntax correctly then this: linear-gradient(transparent 2px, hsla(0,0%,100%,.15) 2px, hsla(0,0%,100%,.15)); basically specifies a gradient that is transparent from the top to 2px down, then is hsla(0,0%,100%,.15) from 2px down to the bottom. If that is correct, then there is no point in using a gradient. Simply create a box that starts two pixels from the top and fill it with the color hsla(0,0%,100%,.15). But then if we can do that, then we don't need the 'foreignObject' in order to be able to use 'background-image'. We can simply use an SVG <rect>. And if we can just use an SVG shape, then we don't need the 'clipPath' (expensive) and can just make the shape a path that has the outline of the clipPath. So unless I'm wrong about the gradient, then the only thing we need in this SVG is a single <path> element with a fill.
Is this worth looking at, or is this code being replaced for Photon?
Yes, we're definitely removing the tab curve in bug 1349555 very soon and I think that also means getting rid of these SVGs. So I'll mark this as WONTFIX, meaning we'll not optimize the SVGs right now but will hopefully get rid of them in bug 1349555.