Mozilla added Click to Play plugins feature to Firefox 14 but not enabled by default, we don’t know which Firefox version gets UI for this option in Options but we can enable click to play preference in Firefox right now through about:config in Firefox 15 and other channel versions of Firefox by setting plugins.click_to_play preference value to true and other channel versions of Firefox and activate plugins on demand so that to load any plugin content you just need to click it.
There may be a case where sometimes you don’t want to enable plugins on demand then you’ve to visit about:config and need to disable that preference, without this hassle you can install Click to Play Switch add-on for Firefox which adds button at the end on navigation bar which you can use to toggle plugins.click_ to_ play setting on or off with a click.
After installing the extension, on restart this add-on will set click to play preference value to true. Once any page with plugin content like Flash is loaded in Firefox you need to click on that to activate, you can set the preference to off by clicking on icon on navigation bar, if you select “reload tab on click” option for extension in its options then you don’t even need to reload the tab after clicking the button for the changes to take effect.
You may encounter an issue with this extension where its button doesn’t appear after install on navigation bar, hover your pointer and click on blank space below close button of Window on navigation bar for the button to appear.