Метод 1:
http://forums.mozillazine.org/viewtopic.php?t=206216

Complete Embedded & Streaming Quicktime/Real/Windows Media Player Guide for Windows Users.

Contents
Media
Warp to Introduction
Warp to Media Player Plugins and Missing Plugin Alert
Warp to Audio not playing, but no Missing Plugin Alert
Warp to Letting Firefox Claim it is Internet Explorer
Warp to Viewing Launch.com video
Warp to Download files instead of opening in browser
Warp to Stream files instead of downloading
Warp to If all else fails...
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This media player info here is still being maintained, but it has also been mirrored in the mozillaZine Knowledge Base: http://kb.mozillazine.org/Video_or_audio_doesn%27t_play

Introduction
When surfing the web, it is common to find embedded audio and video that uses Windows Media Player, Quicktime, or Real Player. There are Netscape plugins available for all 3 (usually installed into Firefox when their respective player is installed) that work with Firefox, but compared to the Internet Explorer plugins they are limited and do not always work. In addition, many websites use IE-only techniques (as opposed to standard code, which is supported by all browsers) to embed media.

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Media Player Plugins and Missing Plugin Alert
MozillaKine Knowledge Base article: http://kb.mozillazine.org/Video_or_audio_doesn%27t_play

The three basic media players (Windows Media Player, Quicktime, and Real Player) all have a browser plugin. This allows a browser such as Firefox to open a small media player window inside a web page. Installing a media player does not necessarily mean you also install its plugin - so if, for example, you have Windows Media Player installed and you still get a missing plugin alert on a web page that has a windows media file embedded in it, then you likely lack the Windows Media Player plugin. In addition, there are known issues with each plugin as well as ways you can configure them to make them work better. The following guides are available to help you solve these problems:

Embedded Real Player/Real Alternative by _Jim_
Embedded Quicktime/Quicktime Alternative by _Jim_
Embedded Windows Media in Firefox by Vectorspace
Embedded Windows Media/Launch.com (Firefox 9.x and 1.0PR) by Vectorspace

In addition, it is more common now for websites (such as Google Video) to use the Flash plugin to embed video clips. The Flash plugin can be obtained from here:
http://plugindoc.mozdev.org/windows.html#Flash
Click 'Download' to download the full intstaller - it is more reliable than the online installer.

Quicktime vs. Windows Media Player
If you have the necessary plugins and get missing plugin alerts, then its likely that there is a media file that none of the plugins is configured to play. The usual solution has always been to follow the Quicktime Guide to associate those file types with the Quicktime plugin. A user's preference would usually be to associate them with the WMP plugin, but WMP has no provision for changing the file types associated with its plugin.

Now, there is an alternative. Greasemonkey is an extension that lets you to add bits of JavaScript (known as "user scripts") to any webpage to change and customise it's behavior. I've written one called IE Media Mimic: It looks at all embedded media on all web pages, and the ones that (I think) IE would use WMP to play, are modified to open with the WMP plugin, and to play in Firefox more like how they would be played in IE.
At the time of writing, I do not consider it user-friendly enough yet for the average Firefox user, so read the information on its webpage thoroughly before you consider using it.
Since it is still a work in progress, I would appreciate feedback on how good/badly it works (which you should do here:
http://forums.mozillazine.org/viewtopic.php?t=327437). It also might be updated frequently, so check the version number every now again to see if there is a newer one available. The current verison is 0.8.4. Remember, it requires the Windows Media Player plugin to work so make sure you have it.

Plugin/Extension Conflicts
Some extensions can interfere with the media player plugins - hiding them or preventing them from loading at all. Extensions that conflict with with individual plugins are listed in that plugin's guide.
Adblock
Under Firefox 1.5, Adblock will hide all embedded media - Quicktime, Real Player, Flash, and Windows Media Player - if its OBJ_TABS setting is enabled. The media player will still play if it is set to autostart so sound bay still be audible, but the controls and video image will be hidden. Either disable the OBJ_TABs setting or uninstall it and use Adblock Plus instead.
Amazing Media Browser
This extension has a setting that is enabled by default, to block all embedded objects. For media to work you need to disable that setting or uninstall the extension.
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Audio not playing, but no Missing Plugin Alert
MozillaKine Knowledge Base article: http://kb.mozillazine.org/Background_music_doesn%27t_play

If a page fails to play embedded audio but you do not get a 'Missing Plugin' alert, then it is possible that the page uses the non-standard 'bgsound' tag instead of the 'embed' or 'object' tag to embed the audio file. There are several ways you can make these pages work, Though I recommend you also e-mail the webmaster for the page and ask him to change it.

You can install the 'BGM Conductor' extension from here: http://www.extensionsmirror.nl/index.php?showtopic=369
This extension changes all bgsound tags to embed tags when you view the page, allowing Firefox to detect the embedded audio. While this extension will work in Firefox 1.5.x.x, it needs to be modified slightly before it will install. Instructions on how to do that are here: http://kb.mozillazine.org/Updating_extensions#Updating_incompatible_extensions_for_a_new_application_version

Another option is the aforementioned Greasemonkey script IE Media Mimic, which will (among other things) convert bgsound tags to embed tags. NOTE: At the time of writing, the author of IE Media Mimic does not yet consider it user-friendly enough for the average Firefox user - read the info on its homepage thoroughly before you consider using it.

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Letting Firefox Claim it is Internet Explorer
MozillaKine Knowledge Base article: http://kb.mozillazine.org/Video_or_audio_doesn%27t_play

Some web pages deny you access entirely unless you use Internet Explorer, often because they haven't bothered to test on other browsers, or because they think it only works in Internet Explorer. You can use the User Agent Switcher extension to trick them into thinking you're using IE which may let you into the website, but it it is no guarantee that the website will work.

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Viewing Launch.com video
MozillaKine Knowledge Base article: http://kb.mozillazine.org/Yahoo%21_Music_videos_don%27t_work

Launch.com requires the ActiveX plugin for it to work in Firefox. See the latter half of the Embedded Windows Media in Firefox guide for instructions on how to install it.

Launch.com radio (LAUNCHcast) uses too much IE-only javascript, and by all indications will not function in Firefox. At least, no-one yet has been able to get it to work.

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Download files instead of opening in browser
mozillaZine Knowledge Base Article: http://kb.mozillazine.org/Changing_media_handling_behaviour

With most media files, if you click a link to them you will be prompted to download them. For media files associated with some plugins (Acrobat, Quicktime, Windows Media and Flash files, for example), they will open automatically inside a browser window or in an external player instead.

If you wish to change this behaviour:
Firefox 1.0.x
Go into Firefox Options, and in the bar on the left click the Downloads icon. Click the 'Plug-Ins' button that is below the 'File Types' box, to reveal the list of file types that will open in the browser with the associated plugin instead of downloading. Disable the desired file types by clicking on the checkmark and they will give a download prompt instead. This will not effect media embedded in a web page - only links to the files themselves.

Firefox 1.5.x.x (Including Deer Park, the 1.5 Betas, and the 1.5 Release Candidates)
Go into Firefox Options, and in the top bar click the Downloads icon. Under 'Download Actions' click the 'View & Edit Actions' button to reveal the list of file types that will open in the browser with the associated plugin instead of downloading. Select a file type that you would rather have download or open with an external application and click 'Change Action...'
*If you want the file to open with the default external program for that file type, select "Open them with the default application"
*If you want the file to open with an external program other than the default, select "Open them with this application" - you will then be prompted to select the application to open them with.
*If you want the file to give a standard Open With/download to download prompt then select 'Save them on my computer'


Note: some of the file types listed there (such as all file types associated with the Windows Media Player plugin like .wma, .wmv, etc), if enabled/set to open with the plugin will, when clicked, automatically download and open the file with an external program instead of playing in the browser.

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Stream files instead of downloading
mozillaZine Knowledge Base Article: http://kb.mozillazine.org/Streaming_media_%28Firefox%29

In both Internet Explorer and Firefox, you can click a download link and have the browser open the file in a program, instead of just donwloading it to a specified location. In the case of media files however, IE can have a media player stream the file whereas Firefox will still download the file first before opening it (or Firefox will open it in the browser with the associated plugin, if there is one).

Firefox can duplicate IE's behaviour in several ways. One is with the DownloadWith extension. It is an extension that lets you choose another program to download a file by right-clicking on the link . If you specify a media player for a media file type, then the player will stream the file.
Install the enhanced version of the extension from here: http://www.extensionsmirror.nl/index.php?showtopic=203
And use the sample downloader settings that correspond to the media player that you use: http://downloadwith.mozdev.org/configurations/configurations.xml
While this extension will work in Firefox 1.5.x.x, it needs to be modified slightly before it will install. Instructions on how to do that are here: http://kb.mozillazine.org/Updating_extensions#Updating_incompatible_extensions_for_a_new_application_version
It can be configured to automatically stream links, but I haven't figured that out yet.

The Launchy extension will also allow this. When you right-click on a link, Launchy will provide you with a list of external programs that you can use to open the link. Right-click on a link to a media file, and you can open it directly with a media player without downloading it first.
The extension can be obtained from here: https://addons.mozilla.org/extensions/moreinfo.php?id=81
If you want to use an external application that Launchy does not list, see its homepage for instructions on how to add it.

A third method is to follow the Quicktime Guide to associate the desired file types with the Quicktime Plugin. When you click on a link to such a file, Firefox can use the Quicktime Plugin to stream it within a browser window instead of prompting you to download it. Once it has fully downloaded (once the slider is fully grey) you can just click File > Save Page As to save the file.

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If all else fails...
Despite the web standards and all these guides, many sites have embedded media that will only work in Internet Explorer. If a media file has been embedded using too much non-standard html/javascript, then it will not play in Firefox no matter what you do. This is unfortunate, but there is nothing to be done but use Internet Explorer to view the page in question. Of course, convincing the webmaster of the site to start supporting Firefox can't hurt...

 

Метод 2
http://tragicallynull.com/2006/08/18/missing-windows-media-player-plugin-for-firefox/