Firefox only (Windows/Mac/Linux): The Auto Dial Firefox extension automatically places shortcuts to your most frequently visited web sites inside all of your new, empty tabs. Mozilla Labs recently suggested that empty tabs could be put to better use by offering no-cost options for the user (i.e., if what you want isn't what's offered, it doesn't hurt anything). Although not as inspired as the undeveloped concept at Mozilla Labs, Auto Dial fits perfectly with this idea. If you want more control over the content built in to new tabs, check out the previously mentioned Speed Dial extension. Auto Dial is free, works wherever Firefox does.