"If there are plug-in features which are not available in the Web platform, we encourage developers to post their use cases to mozilla.dev.platform project list, so that Mozilla can prioritize Web platform work to make those use cases possible," he said.
Firefox will ask users whether they want to run browser plug-ins, such as Microsoft's Silverlight or Apple's QuickTime. The browser can be set to always permit a particular Web site to run a certain plug-in.
Mozilla has dealt another blow to those who want to use plug-ins to extend the browser's capabilities. It's keeping all but Flash Player deactivated by default in a version of Firefox now under development.
With the click-to-run plug-in feature, announced in January, plug-ins such as Silverlight and QuickTime won't run unless the user authorizes it when a Web page using them loads. That feature now is built into the Aurora version of Firefox that will grow into the final release in coming weeks. The plug-in hurdle doesn't apply to Adobe Systems' Flash Player, by far the most widely installed and used plug-in. However, the new Firefox can be set to not run it by default.
Mozilla's move is a new step in a wider movement among browser makers to rid the Web of plug-ins, which were useful in a time when browsers rarely released new programming interfaces for new features. However, now plug-ins are viewed largely as security and stability risks, which is why Chrome will begin barring many plug-ins starting in January 2014 and Microsoft banished plug-ins from Internet Explorer running on the new Windows 8 interface. Like Mozilla and Google, Microsoft carved out an exception for Flash, but others -- including Google Talk, Java, and Adobe Acrobat -- will require permission.
"Plug-ins are now a legacy technology," said Benjamin Smedberg, Mozilla's engineering manager for stability and plug-ins, in a blog post Tuesday. "Plug-ins used to be an important tool for prototyping and implementing new features, such as video and animation. As browsers have advanced, this kind of feature development can occur directly within the browser using technologies such as WebGL, WebSockets, WebRTC, and asm.js."
Even those who like plug-ins can't use them in the fast-growing market of mobile devices.
Programmers should start weaning themselves from reliance on plug-ins, shifting instead to Web standards built directly into browsers, Smedberg said.