Thousands of people, including myself, cried out in terror when Google removed the “Side Tabs” from Chrome. I tried for one month to settle into Firefox + Firebug + Tree Style Tabs as my main browser, but that combination is nowhere near is snappy as Chrome for my workload.
My workaround has been to use the most recent build of Chromium (Chrome’s open-source alter ego) that still contained the Side Tabs feature. Because there are no security updates available for this version, I use NoScript and whitelist scripting on sites as needed.
A major advantage of using Chromium instead of an old version of Chrome that has Side Tabs is that Chromium can be run side-by-side with the latest version of Chrome.