Chrome: If you're reading a gigantic article in Chrome, it's easy to get lost and lose track of where you're at. Scrollbar of Contents is an extension that provides you a guide to find what you're looking for quickly by adding markers to the scrollbar.
Scrollbar of Contents pulls header information from articles to provide you with a way to quickly navigate around from the scrollbar. So, if you're on a Wikipedia article and want to quickly jump to a section, hit Shift+Alt+N to reveal Scrollbar of Contents, and then instantly pop down to where you want to go. It doesn't work on every site, but it's incredibly helpful to have around for the supported sites.