When Chrome first came out, the lightweight, clean and out of your field of view tab bar was a welcome change.
FF did pretty good with small changes that, in my view, have made it look better over the years.
edit : Ok, checked the new design. Definitely don't like the tab buttons, mainly because when there are multiple open, there are no discernable borders among them. So a tad bit confusing.
Mine looks like:
@-moz-document url("chrome://browser/content/browser.xul") { #TabsToolbar { visibility: collapse !important; } }
#main-window[tabsintitlebar="true"]:not([extradragspace="true"]) #TabsToolbar > .toolbar-items { opacity: 0; pointer-events: none; }
#main-window:not([tabsintitlebar="true"]) #TabsToolbar { visibility: collapse !important; }
#sidebar-box[sidebarcommand="treestyletab_piro_sakura_ne_jp-sidebar-action"] #sidebar-header { display: none; }
#titlebar { visibility: collapse; }
At the same time I like how the tab bar is separated from the address/bookmark bar. Makes it much easier to identify the active tab.
Especially when you have dozens of tabs, the current style make it cleaner.