OP - explain to me why you would rather have a multitude of separate windows open rather than all your webpages consolidated in your browser?
Do you not like Excel, either? Or NoteTab? Tabbing is a prominent interface style in programs and operating systems alike, just take a look at dialog boxes - most of them are arranged in tabs.
The only possible explanation I could see is that tabs, in Firefox at least, cannot be arranged in tiles, horizontally, or vertically like separate windows, but a browser with tabs is still capable of being opened in separate instances.