Which one gives you a better performance? Is it better to have multiple tabs open in one window or just have multiple Windows open? The Firefox Guru did all of the scientific work on this one, and has found out the results for us.
Over on Go Firefox!, an interesting question was posted: Which uses less system resources (memory)?
My theory is using tabs would use less resources then having the same sites opened in separate windows. My reasoning is each window has to load the entire browser interface, not just the page content. So, I did a little experiment. First using Firefox 22.214.171.124 with a clean profile (no extensions, no plug-ins and default theme) and imported my bookmarks from another profile.