Like most other readers here, my initial reaction is "Thanks, I hate it." I especially hate the assertion that they're increasing customization when in reality they've steadily been removing/hiding real customization options (e.g. compact theme, UrlBar.preventClickSelectsAll).

But, on further consideration I see the value. This feature isn't for power users. The goal of this feature is to increase chances that normal everyday users will make Firefox their daily-driver browser. For many people, having a custom colored browser will be a deciding factor to keep them using Firefox. This is why they didn't call it "themes", which is a techy word that would cause many people to gloss-over and ignore it altogether.

And, in reality, Firefox is still the most customizable browser for power-users. This feature doesn't remove userChrome.css, it doesn't stop users from editing thousands of options via about:config. It doesn't prevent hardcore power users from editing omni.ja to restore preventClickSelectsAll functionality.

So frankly, I hope this feature can help increase Firefox's market share by even a little bit. The more people using Firefox - even if they're not power-users - the better for the future of the open web.