In the Location bar, type about:crashes and hit Enter. Click the link to the most recent one and it'll take you to a site with troubleshooting suggestions.

You can also try starting Firefox in Diagnose Firefox issues using Troubleshoot Mode. It it works without crashing, then one of your add-ons is the culprit.

I've been running the webcam at the link you provided while I've been typing this message, but it hasn't crashed yet.

Thanks Xircal for your reply. I did "about:crashes" and troubleshooting said "Found 0 results for mp4sdecd.dll in English. I started Firefox in Safe Mode and had no problems with this sites web cam. I even opened 4 different windows of the web cam and there were no crashes. There was no sound but I realize not everything works in safe mode. Before I submitted this problem I went to add-ons and disabled different plug-ins and the site still crashed. When running Task Manager in normal or safe mode I'm getting high cpu usage for plugin-container.exe. About 97-100% usage. I'll go back to add-ons and see if disabling any of them help. Maybe I overlooked one of them.

That file appears to belong to Windows Media Player. It's listed in this Microsoft Security Bulletin: MS10-062: Vulnerability in MPEG-4 Codec could allow remote code execution

I just downloaded that critical update from the Microsoft page plus it was automatically updated Wednesday September 15 2010. The site is still crashing and it still reads mp4sdecd.dll. The Microsoft page suggested I run Mats_Run Codec and it removed the Indeo Audio Codec. I use Trend Micro Internet Security and that has't come up with anything. I'll disable it and try the Microsoft Security and see if that picks up anything. Thanks again Xircal,I'll keep working on it. My Son's pc doesn't have a problem with this site.

What did the link in about:crashes say exactly?

By the way, when I go to that webcam site it tells me that I need additional plugins to view the page. Did you see that?

I didn't install them, but can still view the sea (looks a bit murky).

Maybe the additional plugins allow you to move the camera around or something.

Also, they have an email address on the site which you could pose questions to.

Firefox 4.0 Crash Report [@ mp4sdecd.dll@0x3ad12 ] Search Mozilla Support for Help ID: 1d357c6e-8da9-4c79-9094-2feb92110406 Signature: mp4sdecd.dll@0x3ad12

   Details
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   Raw Dump
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Signature mp4sdecd.dll@0x3ad12 UUID 1d357c6e-8da9-4c79-9094-2feb92110406 Process Type plugin Version: Filename: np-mswmp.dll Time 2011-04-06 08:50:24.946080 Uptime 7 Install Age 1251786 seconds (2.1 weeks) since version was first installed. Product Firefox Version 4.0 Build ID 20110318052756 Branch 2.0 OS Windows NT OS Version 5.1.2600 Service Pack 3 CPU x86 CPU Info AuthenticAMD family 15 model 15 stepping 0 Crash Reason EXCEPTION_ACCESS_VIOLATION_WRITE Crash Address 0x5588000 User Comments App Notes AdapterVendorID: 1002, AdapterDeviceID: 9596, AdapterDriverVersion: 8.620.0.0 D3D10 Layers? D3D10 Layers- D3D9 Layers? D3D9 Layers- Processor Notes EMCheckCompatibility False Bugzilla - Report this Crash Crashing Thread Frame Module Signature [Expand] Source 0 mp4sdecd.dll mp4sdecd.dll@0x3ad12 1 mp4sdecd.dll mp4sdecd.dll@0x24971 2 mp4sdecd.dll mp4sdecd.dll@0x1daad 3 mp4sdecd.dll mp4sdecd.dll@0x16c04 4 mp4sdecd.dll mp4sdecd.dll@0xb844 5 mp4sdecd.dll mp4sdecd.dll@0x7636 6 mp4sdecd.dll mp4sdecd.dll@0x975e 7 mp4sdecd.dll mp4sdecd.dll@0x9c9b 8 mp4sdecd.dll mp4sdecd.dll@0xa000 9 WMVCore.dll WMVCore.dll@0xb41a7 10 WMVCore.dll WMVCore.dll@0xbab89 11 WMVCore.dll WMVCore.dll@0xbb310 12 WMVCore.dll WMVCore.dll@0x69b80 13 WMVCore.dll WMVCore.dll@0x6f3cc 14 WMVCore.dll WMVCore.dll@0x651f4 15 WMVCore.dll WMVCore.dll@0x669f8 16 WMVCore.dll WMVCore.dll@0x670b9 17 WMVCore.dll WMVCore.dll@0x67303 18 WMVCore.dll WMVCore.dll@0x64a81 19 msvcrt.dll _endthreadex 20 kernel32.dll BaseThreadStart

I don't get the message additional plug-ins needed. I'm not sure if this is the about:crashes info you want. Found 0 results for mp4sdecd.dll in English is what I get when I go to "Search Mozilla Support for Help". The add images wouldn't take the screen shot of the report so I had to copy and paste it.

What you could try doing is go to Tools | Add-ons and disable the Windows Media Player plugin.

Then go to Download Plugins and download a new copy of WMP. That will overwrite everything you have installed at the moment which belongs to the player.

Alternatively, change the application player to VLC which will play almost anything. The setting is located in Tools | Options | Applications. Click the appropriate player to get the dropdown menu and then choose VLC. Screenshot attached to illustrate where you should be.

Went to Download Plugins and the options were "Change" "Repair" "Remove" and I chose repair since it didn't offer to download a new copy. No luck there. I don't have the "VLC" as one of my player options. It does show the Windows Media Player as the default so I chose that and still had no luck. Off to work and I'll continue working on this tomorrow. Thanks Xircal.

Sorry, should have thought of that. You can download VLC player from http://www.videolan.org/

You can download WMP from here: Download Windows Media Player

Nothing working yet as far as getting that link not to crash. Did a mp4sdecd.dll search and it came up 3 times. For some reason I can't get the screenshot thumbnail to attach so you can read it clearly. I'll keep trying to get a readable thumbnail. For some reason my back slash isn't working on my keyboard or I would type them.

Just a thought. Could you check your firewall logs and see if you can see this entry anywhere: C:\Program Files\Mozilla Firefox\plugin-container.exe If it appears in the log, is the firewall blocking it from accessing memory?

Here is the latest,besides me going nuts trying to get this we cam not to crash and working nights!. I downloaded VLC Media Player and if I copy and paste the address in open network stream the web cam plays with no crashing. Right now I'm trying to get it to play with sound. What I found interesting though is the web cam crashes on all browsers with the same error message:"The Microsoft Windows Media Player Firefox Plugin Has Crashed". Your right ,the VLCMedia Player plays everything. Now I'll just keep going into tools to find out which Audio File matches the web cam played on VLC. Thanks Xircal!

Sounds like you're having a hard time of it.

This link might be of some use to you: http://kb.mozillazine.org/Windows_Media_Player

It is possible that you are infected with malware.

Do a malware check with some malware scanning programs.
You need to scan with all programs because each program detects different malware.
Make sure that you update each program to get the latest version of their databases before doing a scan.

• http://www.malwarebytes.org/mbam.php - Malwarebytes' Anti-Malware
• http://www.superantispyware.com/ - SuperAntispyware
• http://www.microsoft.com/windows/products/winfamily/defender/default.mspx - Windows Defender: Home Page
• http://www.safer-networking.org/en/index.html - Spybot Search & Destroy
• http://www.lavasoft.com/products/ad_aware_free.php - Ad-Aware Free

See also:

• "Spyware on Windows": http://kb.mozillazine.org/Popups_not_blocked

Well still working on this problem. I've done everything suggested. No Malware etc. I disabled-enabled every thing one by one. With just the Windows Media Player plugin enabled it still crashes. Can I remove the plugin besides disabling it and writing over it and reinstall it? The only options I get from the down loader are "Change" "Repair" "Remove" . It doesn't give a reinstall option. I've also been on all the Firefox troubleshooting pages and trying some of the suggestions there. Thanks for all the help so far.