Hey there,

No worries, I got you covered! To adjust the cache size in Firefox 78.15.0 ESR:

Type 'about:config' in the address bar.
Search for 'browser.cache.disk.capacity.'
Double-click it and set your desired size (e.g., 50MB = '51200').
The optimal cache size varies, but 50MB to 250MB should do the trick!

Keep your hard drive happy by clearing the cache and using disk cleanup tools.

Happy browsing! If you need more help, just ask!