This is added now because the original posing interface offers no image upload option.

Further development: Happening at the same time on a different site, Netflix, a streaming failure. After a little system tweaking SyFy will now stream video, but it jerks and freezes, is still most unsatisfactory, and both sites are problematic with both Firefox and Internet Explorer, so it appears that Firefox is not at fault.

Silverlight FINALLY installed (and was recognized as such), but it only streams for like ten seconds, no matter what browser I use, and then the video output portion of the webpage goes black, no video or audio, nor error messages. (This was covered in a Live Chat session…fruitlessly.) Deleting the Silverlight cache contents doesn't do anything, uninstalling and reinstalling it is inefficacious, and setting Playback Options to use HTML5 to render video is ignored by the browser, which keeps trying to use Silverlight ANYWAY, and if I disable the Silverlight plugin with HTML5 specified, the browser keeps asking me to install Silverlight. Three comprehensive antivirus solutions inform me that the memory, pagefile, and data files are clean, and rootkit routers report no threats to rout. I'm beginning to suspect that the Evil Empire operating system, Windows 7 Ultimate x64, is itself the culprit. The only logical thing I can do at this point to isolate the issue is to install the latest long-term support release of Ubuntu [Linux] and test Netflix streaming on that platform.

I'll check back to see if someone else more savvy can offer any helpful suggestions (Netflix upper-tier support staff was utterly stymied), and I'll report the results of my experience with the Linux OS after I carry out my experiment.

The "Video format or MIME type is not supported" message means that the video tag with the built-in HTML5 media player is used and not a Flash player.

You can try to set the Boolean pref media.windows-media-foundation.enabled to false on the about:config page to disable the built-in HTML5 media player for some formats like H.264 (MP4).

• You can open the about:config page via the location bar
• http://kb.mozillazine.org/about:config

Thank you everyone for your help. I promised to post an answer here if I found one elsewhere, but, after replacing my mouse (which used no 3rd-party software, only Windows drivers), all mentioned problems vanished and OTHERS as well. I'm almost angry about it, because the solution, while it was somehow implemented without my knowledge or conscious design, eludes me yet, and I refuse to believe that a slow-to-respond right-click action of my mouse was responsible. I mean, REALLY: What does a mouse have to do with whether or not a wireless adapter functions properly enabling me to see my networked printer and regain file-sharing capabilities? More to the point, the standard no-frills USB mouse has nothing to do with video rendering/media codecs! The good thing about all this is now I have more information to deal with issues in the future if and when they arise. The question has been answered, although the answer itself eludes my quizzical grasp.

I forgot to mention that a couple of days ago I discovered that while this issue existed that my browsers had no problem streaming WMV-format video at support.microsoft.com.