Hi bestbudz99, It depends what processes are running. In order to measure performance of the browser you can test out a couple of different web pages of different sizes. In order to decrease this you can also try the following:

1. Please go to [about:memory] and minimize memory. Close the browser and restart Firefox
2. Check if any add ons or extensions are also running memory when Firefox is open for a long time.
3. Too much Ram troubleshooting too much CPU Troubleshooting

Start Firefox in Safe Mode {web link} While you are in safe mode; Press the <Alt> or <F10> key to bring up the tool bar. Followed by;

Windows; Tools > Options Linux; Edit > Preferences Mac; application name > Preferences

Then Advanced > General. Look for and turn off Use Hardware Acceleration.

Poke around safe web sites and see if there is still a problem. Then restart.