Numerous popular web-sites are using Flash, approach that tends to slowdown computers, as well as to carry various vulnerabilities.
Mozilla Firefox nightly build has received an initial implementation of a new default plugin, click-to-play, that blocks the flash content and allows the blocked items to be run only after the user clicks on it, consequently, that particular web-page loads faster, reducing considerably the used computer resources, thus basically the click-to-play plugin presents itself as an on-demand flash blocker.
Although the plugin is in its early beginnings, can be activated in Firefox nightly by typing
about:config in the addressbar, then search
plugins.click_to_play and double-click on it (to make it true).
An exciting part of the probably future development of the plugin is its ability to remember its settings per web-site (meaning, if a user blocks the flash content in 3 web-sites and allows flash running in 1 site, closing and reopening the web-bowser and revisiting the web-sites follows the previously chosen activation settings).