What is new tab and new window?
Assuming that you are asking about Firefox's options "Open Link in new Tab" v/s "Open link in new window" when you right click on any link.Open Link in new TabThis option will open that link in a new tab under same instance of firefox. You can then switch between tabs from tab menu at the top of the browser.Open link in new WindowThis option will open that link in a new instance of firefox. Unlike the New Tab, you will see a new firefox instance in your task manager at the bottom of your screen. You can individually manage(close, resize etc) each window if you use this.