Search your tabs in Safari, Chrome, Chromium, Chrome Canary, and Webkit.
When you action a result, it'll bring your browser to the front and switch to the selected tab. You can also close a tab by holding down alt when actioning a result.
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Updated Feb 8, 2014: Made it more resilient to an AppleScript error that could cause a blank output.
Update #2, Feb 1, 2014: Fixed regression with searching. You should be able to search anchored by words (and capital letters in CamelCase words) again.
Updated Feb 1, 2014: Rewrote the workflow. It now supports copying the URL of a tab, viewing a tab in QuickLook, and closing a tab with a modifier key.
Updated Oct 11, 2013: Fixed issue with improper string encoding in Mavericks and Ruby 2.0 breaking the workflow.
Updated Oct 9, 2013: Updated for Mavericks and Ruby 2.0.0. Removed thumbnails for now (beta versions of Safari don't seem to generate them anymore). Fixed some issues where the proper window wouldn't always focus correctly.
Updated May 4, 2013: Experimental support for webpage thumbnails. Prevent launching browsers when WebKit is open.
Updated Mar 26, 2013: (Hopefully) prevent launching browsers when it's not supposed to, and fix an issue with it not detecting WebKit.