Firefox has issues with memory leaks. It's a great browser, my favorite, but still the memory leaks are annoying. There is one thing that can be done quite easily to help reduce the memory leaks in Firefox though.

In the address bar of the browser, type about:config and hit enter. This will bring up the configuration screen.

In the Filter input, type trim_on. If this brings up a line in the window, double click on the line so that the value (in the third column) is set to True.

If you get an empty page after typing in the filter, right click in the empty window below the filter and select New -> Boolean from the menu that is shown. When asked for the name of the new value, enter config. trim_on_minimize and press Enter.

This will bring up a window that allows you to set the value as either False or True, select True.

Once you do this the window will still be empty. Go to the filter and append an underscore to the filter so that it reads trim_on_. This will cause it to re-filter, and your new entry should now show up in the window below. You can now close this Firefox window.

Setting this value will allow Windows to swap out the Firefox memory that is in use when a Firefox window is minimized. This will result in reduce memory usage overall. The only problem with this fix is that it only works on Windows machines.