Firefox also includes a task manager, which however opens up in a tab, like a screenshot above, which can be accessed under More in the application menu. On Chrome, while in the browser, simply press Shift+Esc to bring up the floating window.
That is why both Firefox and Chrome include builtin task managers. Unfortunately, with tens of pages open it can sometimes be difficult to see which site is causing the slow-down. Web browsers are well-known resource hogs, but it is often poorly coded websites and plugins which are the main culprits.
