As per the latest announcement from Mozilla, In future releases Firefox will be blocking plugins by default. However, most plugins will be available through a “click to allow” feature, at least for the time being. Flash will still be enabled by default.
Read more here, below is the small snippet from blog.mozilla
To give people a better Firefox experience, we’re changing the way plugins work. Earlier this year we talked about our plan for putting users in control of their plugins. We are now seeing these plans take shape in the latest version of Firefox Aurora. To give people more control over their browser, Firefox will no longer activate most plugins by default. When a site tries to use a plugin, the user will be able to choose whether to enable the plugin on that site.