Use Firefox 45.8.0 ESR (Extended Support Release)
Plugins still work for this version.
https://www.mozilla.org/en-US/firefo.../releasenotes/
Who is it for?
https://www.mozilla.org/en-US/firefox/organizations/
Firefox ESR is intended for groups who deploy and maintain the desktop environment in large organizations such as universities and other schools, county or city governments and businesses.
Who is it not for?
Individual users who always want the latest features, performance enhancements and technologies in their browser without waiting for them to become available in ESR several development cycles later.