I've also forgot to mention that if the high CPU usage task runs while FireFox is open, and I end that task, FireFox still remains open and doesn't seem to be affected by it

The screenshot sheds no light because all 'tasks' have the same name. Try Firefox's Task Manager from either menu (Tools on the menu bar or More tools in the other menu) (or about:performance in the address bar). You may have permitted Data Collection and Use in Settings (Privacy & Security page). https://support.mozilla.org/en-US/kb/firefox-uses-too-much-memory-or-cpu-resources

Here is another screenshot, the task manager of Firefox seems to show nothing is using much memory, but in the Windows Task manager it does, if I go to the details of the task, and I click "Open file location" on the high CPU usage Firefox task, and it's the main Firefox application in the main Firefox directory (C:\Program Files\Mozilla Firefox\Firefox.exe), my thought was maybe a malicious file is running in the background and disguising itself as Firefox, but it doesn't seem to be the case