It's FOSS published a tutorial about how to use the Firefox Task Manager to find and kill RAM and CPU eating tabs and extensions.

How to Use the Firefox Task Manager (to Find and Kill RAM and CPU Eating Tabs and Extensions)

What's causing Firefox to slow down or use too much RAM and CPU? Analyze tabs, scripts and other processes with the built-in task manager in Firefox.

How to Use the Firefox Task Manager (to Find and Kill RAM and CPU Eating Tabs and Extensions)