I only noticed this rather recently.. But you can set up Firefox’s ‘Homepage’ option to open multiple tabs when you open the browser.
Just enter the URLs you want to open by default, separated by the pipe (’|’) character. The same effect can be achieved by opening all the tabs you want, then use the ‘Use Current Page(s)’ button.
So you can now open Google and 200 random websites you probably won’t even look at anyway! Personally, it irritated the hell out of me, but maybe someone would find it useful…