I use tabs heavily when browsing, i see something interesting and ctrl click and carry on reading whit it loads in the background so for me the speed of loading isn't as important as the ui. i think that with the way i browse firefox is already much faster. The way i check my notifications in facebook, for example - i'll ctrl click each one and then check out the tabs. much quicker than clicking one, pressing back waiting for the page to reload, click the next, etc...