For sandboxing purposes, we would like to stop calling OS APIs for theme drawing from the content process. The intention is to achieve this via bug 1535761, which will switch to non-native form control drawing.

However, we would still like scrollbars to look native on each OS. Scrollbars are drawn inside the content process (even the root scrollbar), so the plan is to emulate native-looking scrollbar drawing for each platform with custom drawing.

Tracking non-native theming bugs for Fission Beta milestone (M7).

Only Linux NNT is a Fission blocker and this is not marked as a linux-nnt blocker so removing the Fission milestone here. If this turns out to be required for Linux-NNT, please add Fission Milestone ? to add it back to Fission triage. Thanks!