Download this add-on STIG from the Forge.mil site
Install it, and under options, click on APPLY STIGs. Then it should be secure enough. I dont think its the FULL version STIG though, but a nice free Add-ON to have for FF. I have this too, and it does warn you that it might "break" things, but so far everything works smoothly.
The site is also maintained by DISA.