Once bug 1988635 lands, if a user is in forced-colors mode, they will be able to change themes in about:addons, but the browser appearance will not change. We want to show a message to forced-colors users warning them that themes are disabled in forced-colors mode. Note that a message-bar was added to about:addons as part of the colorways removal work; see https://phabricator.services.mozilla.com/D243450 for details. We can reuse that message-bar to show our message. Before engineering work can begin, we will need final content changes here from :emilyw and kbryant.
Bug 1988637 Comment 0 Edit History
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Once bug 1988635 lands, if a user is in forced-colors mode, they will be able to change themes in about:addons, but the browser appearance will not change. We want to show a message to forced-colors users warning them that themes are disabled in forced-colors mode. As with bug 1988635, the change here should be wrapped in a pref-backed Nimbus Variable in case we need to remotely disable it; we should use the same Nimbus Variable defined in bug 1988635. Note that a message-bar was added to about:addons as part of the colorways removal work; see https://phabricator.services.mozilla.com/D243450 for details. We can reuse that message-bar to show our message. Before engineering work can begin, we will need final content changes here from :emilyw and kbryant.