Those who lived through the tabbed browsing revolution will remember just how convenient it felt to be able to open up three or four tabs in the background without losing focus from the current one. Now that kind of behaviour is taken for granted, but if you queue up too many tabs to get around to later it can start to put pressure on your browser.
RAM can get squeezed, battery life can drop and your CPU can start working overtime if the system has half-a-dozen feature-rich websites to juggle at one time. The solution is to open up new tabs silently, which essentially loads the URL in the background and nothing else -- only when you switch to the tab in question is the page loaded.
There's a new extension on the Firefox block that brings this functionality to Mozilla's browser -- the aptly named Open Link in Silent Tab is still in the early stages of its development, but it works as advertised. Let's hope similar tools are on the way for other browsers, as it can be a very handy option to have on slower machines or more media-heavy websites.