Re: This is a distraction!
Firefox (and Thunderbird to a lesser extent) need add-in/ons now to be actually usable, Classic Theme restorer allows most nonsense to be fixed. You STILL have to edit About:config to fix the stupid "Awesome bar" to be a sensible URL entry and the search box to be usable. An application should use the styles, themes etc of GUI the OS I've chosen and configured, not some half baked Kool-aid version.
Sorry, but what the HELL to Mozilla know about designing an OS? Or is it like Android, a variation of Linux (Android adds a Google Binary blob (if you want Playstore Access), Davik instead of Java VM and Android GUI to what is mostly Linux).
We have Linux (with a variation for TVs, OpenWRT or DDwrt for Routers etc), Android, iOS, the child of Fingerworks + OS X (derived from BSD). QNX (used in loads of non-phone embedded stuff before RIM bought it), VX Works
Moribund: Palm, Blackberry, Symbian
Various flavours of non-desktop Windows, based on DOS/Win3.1, Win CE and Win NT.
Even variations of CP/M, Forth, DR MultiDos etc.
What exact market need or problem other than Mozilla ego is a "Firefox" branded Embedded OS supposed to solve?