The extension does not require containers. The container-related scope options ("Container in active window", "Container in all windows") are optional and only relevant if you already use Firefox Multi-Account Containers. The default scope ("Active window") works without any container setup.

The keyboard shortcut conflict you describe is caused by the Multi-Account Containers extension itself, not by Duplicate Tabs Closer. If you deactivate the Multi-Account Containers extension (or simply leave the scope set to a non-container option in DTC), there should be no conflict.

If you are still on this version and the issue persists, feel free to open a report at https://github.com/Peuj/duplicate-tabs-closer/issues with more details.