"Developers will be able to update their existing NPAPI-based Apps and Extensions until May 2014, when they will be removed from the Web Store home page, search results, and category pages," Schuh said. "In September 2014, all existing NPAPI-based Apps and Extensions will be unpublished. Existing installations will continue to work until Chrome fully removes support for NPAPI."
Schuh also noted that Mozilla plans to start blocking NPAPI plug-ins by default in December 2013 with the release of Firefox 26.
Mozilla already blocks some outdated plug-ins that pose security risks and in January announced plans to block all plug-ins except for the most recent version of Flash Player once its work on the click-to-play user interface is complete. The Firefox click-to-play feature is still in beta testing stages and can only be enabled at this time by accessing the browser's advanced about:config options.
It's not clear if Mozilla also plans to completely remove support for NPAPI plug-ins from Firefox in the future. A representative was not able to immediately clarify the situation.
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