Firefox has always been a popular alternate browser, although its popularity has been declining a bit, since the launch of Chrome. It is the common experience of many a Firefox users, that the browser, over a period of time slows down considerably. It may take a lot of time to load during startup and the overall speed could also be effected.

Firefox has made considerable improvements in the browsers memory consumption and utilization but it still makes people wanting more. In fact, some even prefered to install the Memory Restart or Memory Fox add ons from Mozilla and even considered disabling the slowest Firefox addons.
Speed Up Firefox

I do not normally use Firefox, preferring instead the Internet Explorer, but I do know of five freeware that may help you optimize Firefox and its memory and make it load and run faster.