The goal of this bug is to add the ability to specify a different pageAction icon for light and dark themes as we are currently doing for the browserActions (Bug 1329242), as a follow up to Bug 1397196 which fixes an issue that breaks an extension that contains in its manifest both a pageAction and a browserAction with the same default_icon file name when the browserAction also specify the theme-based icons.

Because screenshots is now a page action, if you've got a dark theme this is a bit more jarring.

I spoke to the screenshots team and the page action is not rendered by a WebExtension, but the bootstrap.js part of the file. A fix is incoming for that on the screenshots project. Dropping priority down accordingly.