So that PB looks its best on people's toolbars and the screenshots they take.

Some unflattering status quo examples here:

https://bsky.app/profile/eff.org/post/3llfcvezfwc2d

Unfortunately, SVG icons are only supported by Firefox (and Safari).

https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/icons

https://issues.chromium.org/issues/41057033

We should be able to improve our icons in non-Firefox browsers too though:

To deliver the best visual experience to users with high-resolution displays, such as Retina displays, provide double-sized versions of your icons.