The newest version has security updates you won't want to skip out on.
Naked Security explains:
The popular web browser released a major update on August 8, version 55, which — in addition to some nifty new features, like Virtual Reality support — includes a number of security fixes. Firefox 55 remediates three critical and 11 high-impact vulnerabilities, as well as seven moderate and six low-impact vulns.
Of the critical and high-impact vulnerabilities fixed, several of them would have allowed an attacker to crash the browser, execute arbitrary code, or even access sensitive information on a page the user was reading. A few days after the 55 release came its first minor update, 55.0.1, which includes a few additional bug fixes.
On August 8 also came the latest major update for Firefox Extended Support Release (ESR), version 52.3.0, which might be of interest to you if you manage and deploy Firefox in an organization. Firefox ESR 52.3.0 also mitigates the same security vulnerabilities as addressed in Firefox 55, all detailed in the MFSA 2017-18 security bulletin.