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Firefox Sidebar and Vertical tabs: try them out in Nightly Firefox Labs 131 – Firefox Nightly News
(blog.nightly.mozilla.org)
This is a most excellent place for technology news and articles.
Finally vertical tabs, have been missing those
I have a custom FF theme that, combined with a tab tree extension, gives me a vertical layout, but it's still kind of hacky. It will be nice to finally have fully supported vertical tabs.
I'm especially hopeful that native support will make those extensions even better.