Uniqueify Chat од MalTeeez

Usage:
To use the extension, while watching a twitch channel, open the popup via the extension icon, and select the mode you want to use to deduplicate messages, you probably want "global" (or hover over the modes for more info).
The selected mode for channels are stored and can be managed via the the list while on twitch.
Permissions:
The extension needs "host_permissions" (for *://*.twitch.tv/*) to modify the twitch page with its annotations and the "storage" permission to make user decisions persistent.