F-Secure SAFE for Mac Browsing Protection broken for Firefox v57 (Quantum)
F-Secure SAFE version 17.1 (16230) for macOS Sierra (10.12.6) Browsing Protection extension for Firefox is broken in latest Firefox v57 a.k.a. "Quantum".
It does not fulfill the new Firefox addon requirements and therefore it is marked as "legacy extension" and disabled by Firefox.
Versions of "Firefox Quantum" have been available in Nightly / Developer channels since early August and in official Beta since late September.
Firefox add-on requirements can be found at https://support.mozilla.org/en-US/kb/firefox-add-technology-modernizing
See these links for more info: