My opinion is to have everything open in a new tab, too many windows = too much clutter, but that is my personal prefrence and is firefox's defualt.

See: Firefox button > Options > Tabs > Open New Windows in new tabs

Thanks for the reply. I'm still not clear on this. Assuming tabs cause less clutter than windows, why is "new window" available?

Because it is a option, and that is my personal opinion (we are not mozilla employees, but volunteers).

Hello winofine,

if you are not working(or viewing) with sessions, example: to see the news for football in different sites, to seek a scientific article for hyperlipidemia in different sites, to find a specific presents in different sites, so, to have the sites more clear and not confused, it is good to open a new window with each session(football, scientific articles, presents)

if you are not viewing that way then it is better to open new tabs

as Waka_Flocka_Flame said above it is personal option, tabs or windows

thank you

Thanks to all!

you are welcome