Meta bug to track the feature work needed to support high contrast mode in DevTools.
Currently DevTools does not support High Contrast mode. Before Bug 1539979, high contrast mode were simply not applied to the toolbox, because the devtools toolbox was loaded in a frame with type=chrome, which means it always kept the authored colors.
Now that DevTools are loaded in a frame with type=content, High Contrast mode colors are applied to the Toolbox, but since the stylesheets of DevTools were not designed with High Contrast support in mind, the end-result is not great yet.
We are currently working on adding an exception so that DevTools are preserved from High Contrast mode once again (bug 1575766).
After that we should add a preference that will allow to toggle the exception, so that we can work on high contrast mode for DevTools (see https://bugzilla.mozilla.org/show_bug.cgi?id=1575766#c22 , bug not filed yet).
Finally we should review the DevTools panels in high contrast mode and fix our stylesheets so that the experience is good in High Contrast mode.
Note that high contrast mode will be improved with Bug 1575689, which should add support for rendering images in high contrast mode.