Plugins are a necessary evil of the Internet. The often vulnerable software plugins that enable video and audio streaming on Web browsers are regularly exploited by hackers. To stop the spread of malware, Mozilla is now moving to change how Firefox handles plugins.

Mozilla announced today that Firefox will soon block most third-party plugins by default. This means that future versions of Firefox will ask your permission to display plugin-enabled content. There permissions will be handled on a per-site basis so enabling Microsoft Silverlight to run on one Netflix video will ensure that all of Netflix will be whitelisted in the future.

It should be noted that Firefox will not be blocking all third-party plugins. It won’t block for Adobe Flash because it’s “so common on the Web.” Mozilla also notes that blocking Flash by default would confuse many users due to the fact that many Web sites use hidden Flash instances all throughout a Web page.

Wait, that’s a little unfair, right? Flash is just as vulnerable as any other plugin, so why does it get special treatment? For starters, Flash is still everywhere on the Web, and a blanket blockade would ruin a lot of Web pages for a lot of people. Besides, Firefox already blocks older versions of Flash while reminding users to upgrade to the latest secure version.

Mozilla may be trying to protect users with this latest move, but that’s not the only reason it’s blocking plugins. The non-profit is known as a strong proponent of Web technologies like HTML5 and has been encouraging developers to dump plugins in favor of it. While HTML5 has certainly made some great strides over the last year, it still can’t match the performance of a plugin like Flash or the Unity Web Player. Until it can, plugins are here to stay.

If you want to try the new plugin blocker for yourself, just download the latest Firefox Aurora release.