Fancy stuff maybe as an option, but not mandatory.
"...why is it so hard to realise that the elegant solution is merging all tab functionality into the system task bar?"
Maybe for some people, as an option that could be turned on if desired, but not if it was mandatory.
It wouldn't work at all for me (which is why I'd want it turned off), because I auto-hide the taskbar in both XP and Linux - the taskbar only becomes visible (temporarily for a few seconds when I pass the mouse over it) only when I actually need it, mostly just as a quick occasional reminder of what other apps/windows/HDD/whatever I've got open at any given moment - easier to see it visually in one glance there instead of Alt-Tabbing through everything - although I usually do use Alt-Tab to actually switch apps.
If Firefox tabs were all on the taskbar, it would horribly compete for space with the other apps' windows/folders/HDD(several)/etc on the taskbar - no way 60 tabs + other apps' windows are going to fit there, nor should they have to. Also I would not want Firefox tabs autohiding, yet I have no intention to turn off the taskbar-autohide feature (I like it).
More space-saving: At the top of the Firefox window, I deleted the entire button bar - I never click those buttons anyway - use keyboard shortcuts instead, I mean seriously, come on, does anyone over the age of 5 actually *click* "Back" or "Home" or "Refresh" etc when keyboard shortcuts are so much easier? I also hid the bookmarks toolbar (I wrote out a quick HTML page of links for that, instead; it's easier), and the address/URL bar is on the SAME LINE as the File/Menu/etc menu things. Deleted search thingie (never use it). So there is far less space wasted at the top of the monitor. But don't EVEN think about taking away my menus! True I use keyboard shortcuts to operate the menus (I'm lazy), instead of clicking them, but I like to have them there anyway. As I said they're on the same line as the URL field, so there would be no space advantage to getting rid of them.
Of course, everyone's aware, right, that you can set Firefox's minimum tab width to less than the standard, to fit lots more tabs on screen (normal top placement), using Firefox's about:config.
I can see having the various options that other people have suggested here AS LONG AS those new options were turn-off-able ;) so that people who wanted the normal UI could use that instead, and people who wanted the fancy new cutting-edge UI could use that.