"You leave the choice to the user, who generally, when presented with a broken picture or a dialog which says click to see the movie, will click it," Raiu said. "Generally, best defenses work by taking this choice away from the user."
Raiu believes that Mozilla should build a click-to-play whitelist for popular websites like YouTube or Dailymotion, so users don't develop a reflex of approving plug-in-based content without giving it much thought.
On the downside, if the feature becomes popular, it is likely to be abused by attackers who could use rogue click-to-play images to trick users into downloading malicious files that masquerade as video codecs or browser plug-in updates.
This kind of abuse has happened in the past with the "What's New" page, which gets displayed after every Firefox update, the Safe Browsing alert page, which appears when users attempt to access known malicious websites, or the Firefox plug-in version check page, where users are informed about outdated plug-ins.
"I'm quite certain that the feature will be abused in social-engineering attacks, however, I don't think the risk outweighs the benefit," Raiu said. Botezatu feels the same way.
"Now is a good time to have a click-to-play feature, given the fact that web-based attacks have increased exponentially and - most importantly - are becoming cross-platform," Botezatu said, pointing to the recent attacks that exploited a vulnerability in the Java browser plug-in to infect over 600,000 Mac OS X computers with the Flashback malware.
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