Yesterday Mozilla made available Firefox 41 and Firefox ESR (Extended Support Release) 38.3.
Firefox 41 resolves 26 CVEs (defined) and 3 issues (not yet assigned CVEs). When broken down the severity of these issues is as follows:
6x critical severity CVEs
11x high severity CVEs and 2 high priority issues
8x moderate severity CVEs and 1 moderate issue
1x low severity CVE
Firefox ESR 38.3 meanwhile resolves 17 CVEs and 2 issues (not yet assigned CVEs):
5x critical severity CVEs
10x high severity CVEs and 2 high priority issues
2x moderate severity CVEs
Full details of the security issues resolved by these updates are available in the following links:
Details of how to install updates for Firefox are here. Mozilla Firefox updates generally install without issues, however as always I would recommend backing up the data on any device for which you are installing updates in order to prevent data loss in the rare event that any update causes unexpected issues.