I've used this extension for doing mass closes: https://addons.mozilla.org/en-US/firefox/addon/sorted-tabs/ https://addons.mozilla.org/en-US/firefox/addon/sorte

I've used this extension for doing mass closes: https://addons.mozilla.org/en-US/firefox/addon/sorted-tabs/ https://addons.mozilla.org/en-US/firefox/addon/sorted-tabs/ As a bonus you can arrange URLs by name, url, or time next to each other, so it's usually fast to churn through related or duplicate tabs.