Just for funsies, I decided to write a script that runs in the background while monitoring active processes. You set how many processes to list and a memory threshold amount. If any process goes over that amount, the program window is displayed.
The program is called MemoryHogs and can be downloaded as either a script file if you have AutoHotkey installed on your computer or an executable version can be downloaded.
In the example below, the window will display the top two process memory hogs and will automatically appear when any process uses over 700 megabytes of memory. As you can see, Firefox is pretty close. You can change both numbers to suit your needs. If you want to keeps tabs on any number of processes, simply choose "Always Show" from the program's right click menu.
Regular executable file. Just run it, no install needed.