Ignore installation prompts, particularly on Facebook

You might have tried viewing a video on Facebook or another social site, only to be prompted to download a special codec or plugin to actually watch it. These requests are almost always spurious, given the wide compatibility of video formats between browsers and operating systems. Basically, if you did not go looking for a piece of software, do not download it, especially from sites that are unfamiliar and that are likely choked with pop-ups and ads.