3 disk cache prefs

see https://github.com/ghacksuserjs/ghacks-user.js/commit/053808ba971dc308640d2f1646fb6dbb126d6c0e

scratchpad-scripts/ghacks-clear-[removed].js

@@ -1,7 +1,7 @@
 /***
  This will reset the preferences that have been removed completely from the ghacks user.js.
 
- Last updated: 22-Apr-2019
+ Last updated: 27-Apr-2019
 
  For instructions see:
  https://github.com/ghacksuserjs/ghacks-user.js/wiki/3.1-Resetting-Inactive-Prefs-[Scripts]
@@ -123,6 +123,9 @@
     /* 67-beta */
     'canvas.capturestream.enabled',
     'pdfjs.enableWebGL',
+    'browser.cache.disk.capacity',
+    'browser.cache.disk.smart_size.enabled',
+    'browser.cache.disk.smart_size.first_run',
     /* reset parrot: check your open about:config after running the script */
     '_user.js.parrot'
   ]