Glims is a plugin for Safari (including the latest beta) that adds a slew of great features to the browser, though the only ones I really care about are undo for close tab (cmd-z!), favicons-on-tabs (they’re shown on top of each tab’s circled x, which appears when you hover over the favicon) and auto-restoration of previous sessions. (Yes, I’m well aware that other plugins offer similar features (e.g., SafariStand, Saft, etc.), but I’m pretty sure none of them offers all three of the features I list above.)