What you are seeing is a feature that Mozilla has enabled in Firefox 26: click-to-play. (It has been available earlier but had to be enabled in
Click-to-play -- a security feature that requires users to authorize the use of a plug-in when a website or page element requires it -- has been adopted by other browsers as protection against a rising tide of exploits that leverage bugs in plug-ins, particularly Adobe's Flash Player and Oracle's Java.
If you really don't want to see this security in action you can, at your own risk, go into
about:addons and, in the plugins tab, change what you want to "Always Activate".
For more information look at Plugin Activation in Firefox written at the time the Aurora version was released:
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.
A plugin is 3rd-party software which is loaded into the browser to assist in rendering the Web. Even though many users are not even aware of plugins, they are a significant source of hangs, crashes, and security incidents. By allowing users to decide which sites need to use plugins, Firefox will help protect them and keep their browser running smoothly.