I eventually installed an additional old version of Firefox (used for testing only) to resolve this, besides my regular (secure, up to date) latest Firefox installation.
This requires webdriver to know where it can find the Firefox binary, which can be set through the webdriver.firefox.bin
property.
What worked for me (mac, maven, /tmp/ff46
as installation folder) is:
mvn -Dwebdriver.firefox.bin=/tmp/ff46/Firefox.app/Contents/MacOS/firefox-bin verify
To install an old version of Firefox in a dedicated folder, create the folder, open Finder in that folder, download the Firefox dmg, and drag it to that Finder.