I'm running the LTS of Xubuntu on an older machine (~2009), and it works great most of the time. However, once in a while, something (pretty sure it's Firefox) starts churning the SSD and slows the computer to such a crawl that the cursor barely responds to the mouse. I haven't been able to close any applications once it does this; my only option is to hit the Reset button or do a hard shutdown. I have maybe 10-20 tabs open in Firefox, not dozens. Anyone have any ideas for fixing this, or mitigating it somewhat?