Honestly, I find that the built-in behavior is good enough: go to the location bar (ctrl-L), type "% <substring>" and it will search through all open tab

Honestly, I find that the built-in behavior is good enough: go to the location bar (ctrl-L), type "% <substring>" and it will search through all open tab titles as an autocomplete thing. It doesn't search tab content (probably good since most tabs won't be loaded), but it's good enough for me most of the time. Great feature, completely undiscoverable.