A single security fix is apparently the sole reason Mozilla released Firefox 52.0.1 on March 17. There was no announcement from Mozilla, but as usual, CERT picked up the slack with their own announcement. The release notes for 52.0.1 point to a related security advisory.

Firefox will offer to update itself over the next few days, but you can usually trigger an update by navigating to its About dialog (hamburger menu icon > question mark icon > About Firefox).