HTML5 H.264 in Windows XP possible?

I recently deleted Adobe Flash from my Windows XP 64 computer because the plugin was locking up both the Firefox 33 browser and the whole computer. I figured I could live with HTML5. The HTML5 in Windows XP does not support H.264. If I want to view a YouTube video, for example, that is encoded using H.264, I cannot watch it in the browser. I must download the video and watch it using Mediaplayer Classic. Since the KLM Codec can handle H.264, is there a way to instruct Firefox to use the KLM whenever it encounters an H.264 video or any other video that the current Windows XP HTML5 cannot display? In other words, can the KLM, or at least the portion handling H.264, be implemented as a plugin by Firefox?

Firefox does not support using external codecs for HTML5 on Windows XP.

You should try again with the latest version of Firefox (33.0.3) and Flash. They fixed a couple of crashes.

If these problems only happened with Firefox 33 and not with 32, then this may help:
In the address bar type: about:config
Set "layers.offmainthreadcomposition.enabled" to false. That is a new feature they added in v33.

The Flash locking up everything (or extremely bogging everything down to the point of it being locked up for all intents and purposes) also happened with Opera. Didn't check it with Internet Explorer so much. I try not to use that except to manually start updates. I'll try that config file edit and let you know how it goes. But I did reinstall the Flash in desperation even though I severely dislike how Adobe is completely OK with third party advertisers doing whatever they like with my IP address. Thus, I will in no way install Adobe Reader again. That's why we have Ghostscript and Ghostview.

SumatraPDF is also awesome.

Updating your graphics driver may help with the Flash problem. You could also try disabling hardware acceleration (there is an option in the right-click menu of Flash).

Thanks. The graphics driver is always as modern as possible (although I have other problems with that, e.g. one particular ATI codec dll (atiokax2.dll) causes Cyberlink PowerDirector to crash on start, so I always have to rename that dll so it does not run.) And I turned off the hardware acceleration a while ago. Have you ever heard about the blind men and the elephant? Or the one about a camel being a horse designed by a committee? Modern computing environments are designed by the biggest committees of all, all the companies that produce all the hardware and software under a strict but hardly enforceable standard. It's really a wonder most of the time that it ever works at all, let alone as well as it does.

You could consider upgrading to Windows 7. That is much more reliable.

I have perfectly functional hardware that has no drivers available beyond XP. I would have to spend nearly $1000 to replace it and obtain a Windows 7 license just to solve a problem with Flash. You tell me if that's worth it. I don't see an up side.