I'm glad you like it. This is one of those personal UX preferences that has you either one or the other camp. Am I right to assume you liked this from your past Opera use?
FLST: https://addons.mozilla.org/en-US/firefox/addon/fww-flst/
It just works. Tab switching is instant, no unnecessary preview, and it has never messed up remembering tab order.
As well as the alt+tab desktop behaviour