I miss when Firefox did minor versions more often. This is just getting rediculous.
tl/dr; summary: 12 months of security only releases. Each year the ESR branch is rebased on the current version of Firefox. I believe Firefox 17 will be the basis for the next year of ESR releases.
Mozilla makes it very difficult to find the download page, but it is here: http://www.mozilla.org/en-US/firefox/organizations/all.html