VLC plugin can be installed from VLC nightly builds. Please be advised that this might be unstable for critical use. Please find the most recent build of VLC-webplugin, and download it. Open the downloaded dmg file, and copy VLC Plugin.plugin to the Internet Plug-Ins directory (/Library/Internet Plug-Ins).
Download the Firefox Extended Support Release 52.9.0 for Mac OS. If you have a newer version of Mozilla Firefox, delete it, and the user configuration data (~/Library/Application Support/Mozilla) using your own discretion. Open the downloaded dmg file, and copy Firefox to the Applications directory. Open Firefox and ensure that the VLC plugin is available to you by going to the URL about:plugins. You should see something like the following screenshot.
In the address/location bar type about:preferences#advanced, and go to General>Update, and select option "Never check for updates (not recommended: security risk)". As suggested this is a huge security risk, and don't use this as your primary browser.
