From the screenshots I have seen which have 3 pages open but only one tab showing,
Active tabs will get the rounded corners, and those not in use will have no background, appearing as just text against the titlebar.
it will be unusable with more than 10 tabs open ..all the text from what used to be an inactive tab will begin to run into text from what used to be the inactive tab next to it ..and so on and so on and so on..how in the hell do they think you'll be able to look for an inactive page to open it..and anyone with less than 20 20 vision is going to keep clicking toolbar elements instead of inactive "pages"..
They should fix what doesn't work rather than playing about breaking what did work..
All because chrome did something..to paraphrase my Gran.."If chrome stuck it's head in the gas oven ..would firefox do the same stupid thing too ? probably" ..Use a Reading accent ( Early.. actually ) to say it ..:)