These are the temporary files saved from your most used websites to perform better and fast loading of the site. You can clear the files and you can also adjust Firefox's settings to Automatically clear the cache. Also you can limit Firefox's cache size. Suppose if you give 500MB space, after every 500MB cache, Firefox will override old files with new caches. To do so:

• Type about:preferences on your address bar, you can also access this page from 3 Bar menu button > Options.
• Then go to the Advanced tab.
• Inside Advanced tab, go to the Network tab.
• Check Override automatic cache management under the Cached Web Content and allocate space you want to give Firefox to store your cache.

Separate Issue; Your System Details shows;

Installed Plug-ins

Shockwave Flash 16.0 r0 Shockwave Flash 21.0 r0 Shockwave Flash 15.0 r0
Having more than one version of a program may cause issues. You must remove the older programs. Then get the current full installer.

Flash: Grab the uninstaller from here: Uninstall Flash Player | Windows Uninstall Flash Player | Mac

Then reinstall the latest version.

Flash Player Version: 20.0.0.306 Note: Windows users should download the active_x for Internet Explorer. and the plugin for Plugin-based browsers (like Firefox).

Note: Windows 8 and Windows 10 have built-in flash players and Adobe will cause a conflict. Install the plugin only. Not the active_x.

https://get.adobe.com/flashplayer/ Direct link scans current system and browser Note: Optional offer: McAfee Security

https://get.adobe.com/flashplayer/otherversions/ Step 1: Select Operating System Step 2: Select A Version (Firefox, Win IE . . . .) Note: Optional offer: McAfee Security

Sashoto Seema. Thanks for the reply with a proper answer, that will most certain help and now I know Firefox can clean it by itself, but with over 3 million files I am just running a command prompt script.

FredMcD. I thought I had uninstalled those previous version, as they do not show up on my control panel and the last time i installed flash it had uninstalled them or so it told me, but I will take your advice.

Thank you both.

Best is to delete the cache2 folder manually with Windows Explorer in cases like this to avoid locking Firefox with deleting that much data. Normally there shouldn't be that much data in the cache folder unless the index files got corrupted possibly because other cleanup software has modified files in the cache.