It's a nice video, with good mockups and sound reasoning. But alas, it's not exactly an innovation. So it kinda looks like an ex post facto justification why they're doing it like Chrome and Opera…
Let's see whether they keep their lead regarding extensions. There are some nice goodies for Firefox that I haven't yet seen in Chrome, Opera or Safari. Some of them even pertaining to tabs (forgot what that color-coded, collapsing mega-tab add-on is called). But the other browsers are catching up quickly, mostly because they make it easier to write extensions. For Chrome and Safari it's basically HTML5 and JavaScript, nobody's royally rogered by XUL.
A a slight tangent: For the last couple of months, I've been using Safari at home without tabs. Expose is great, and it forces me to single-task a bit more. I tend to factor out the "read that later" pages to Instapaper, Evernote and Delicious anyway. Jamie Zawinski ain't that wrong. (On dual screens or without Expose it doesn't work as well, which is why my Linux setup at work is Chrome.)
In my opinion Chrome did Firefox a big favor here.
[Note: I work for Mozilla but I am not on the Firefox UX team and was not involved in this change; these are just my own thoughts.]
If Mozilla 1.0 or even Firefox 1.0 had tabs above the address bar from the beginning, we wouldn't have this problem. But we've spent the last eight years training half a billion people (literally) to use tabs below the address bar. Now most of them have internalized that model and think of as natural, or (much more likely) don't think about it at all but are used to it anyways and will be annoyed if it changes.
(Remember the story about Stuart Feldman in the 1970s when someone asked him to fix annoyances with Makefile parsing? He said it was too late to change the syntax, because Make already had more than a dozen users!)
Mozilla has been debating this for so long because there are good reasons not to change an existing product. Upgrading is more hassle for users when more has changed. Changes to the main UI are the worst.
But users are much more forgiving when adopting a new product like Chrome (not least because the change is less likely to be forced on them). And now that Chrome is so popular, we can point to it as strong evidence that tabs-on-top is a reasonable default that people will be happy to use.
Of course, Firefox still couldn't get away with it without the option to switch back to the old style...
A lot of the video was great and very insightful. But it was pretty funny hearing him talk about the possible problems with putting tabs on top, like your mouse having to travel more, etc. It kinda sounded like they're ignoring the fact that it's been a feature of other browsers for a few years now, and people seem to enjoy it (I do at least).
Let's see whether they keep their lead regarding extensions. There are some nice goodies for Firefox that I haven't yet seen in Chrome, Opera or Safari. Some of them even pertaining to tabs (forgot what that color-coded, collapsing mega-tab add-on is called). But the other browsers are catching up quickly, mostly because they make it easier to write extensions. For Chrome and Safari it's basically HTML5 and JavaScript, nobody's royally rogered by XUL.
A a slight tangent: For the last couple of months, I've been using Safari at home without tabs. Expose is great, and it forces me to single-task a bit more. I tend to factor out the "read that later" pages to Instapaper, Evernote and Delicious anyway. Jamie Zawinski ain't that wrong. (On dual screens or without Expose it doesn't work as well, which is why my Linux setup at work is Chrome.)