hello, could you go to firefox > help > troubleshooting information, copy the contents of that page and paste them here into a reply on the forum? this might give us a clue what is going on...

Application Basics
Name 	Firefox
Version 	26.0
Update History 	
User Agent 	Mozilla/5.0 (Windows NT 5.1; WOW64; rv:26.0) Gecko/20100101 Firefox/26.0
Profile Folder 	
Enabled Plugins 	about:plugins
Build Configuration 	about:buildconfig
Crash Reports 	about:crashes
Memory Use 	about:memory
Extensions
Name 	Version 	Enabled 	ID
Yahoo! Toolbar	3.1.0.20130818030116	true	{635abd67-4fe9-1b23-4f01-e679fa7484c1}
Default Manager	2.2	false	{3252b9ae-c69a-4eaf-9502-dc9c1f6c009e}
GreatArcadeHits Add-on	1.0.0	false	{B21F5E31-B8E8-41CD-B74C-168A71A10E49}
PassShow	1.150	false	{57c20073-e24b-4b2a-aa91-70d1ad526cbf}
Important Modified Preferences
Name 	Value browser.cache.disk.capacity	358400
browser.cache.disk.smart_size.first_run	false
browser.cache.disk.smart_size.use_old_max	false
browser.cache.disk.smart_size_cached_value	358400
browser.places.smartBookmarksVersion	4
browser.sessionstore.upgradeBackup.latestBuildID	20131205075310
browser.startup.homepage_override.buildID	20131205075310
browser.startup.homepage_override.mstone	26.0
dom.mozApps.used	true
extensions.lastAppVersion	26.0
gfx.direct3d.last_used_feature_level_idx	0
network.cookie.prefsMigrated	true
places.database.lastMaintenance	1390321799
places.history.expiration.transient_current_max_pages	104858
plugin.disable_full_page_plugin_for_types	application/pdf
plugin.importedState	true
print.printer_HP_Officejet_6500_E709n_Series.print_bgcolor	false
print.printer_HP_Officejet_6500_E709n_Series.print_bgimages	false
print.printer_HP_Officejet_6500_E709n_Series.print_colorspace	
print.printer_HP_Officejet_6500_E709n_Series.print_command	
print.printer_HP_Officejet_6500_E709n_Series.print_downloadfonts	false
print.printer_HP_Officejet_6500_E709n_Series.print_duplex	0
print.printer_HP_Officejet_6500_E709n_Series.print_edge_bottom	0
print.printer_HP_Officejet_6500_E709n_Series.print_edge_left	0
print.printer_HP_Officejet_6500_E709n_Series.print_edge_right	0
print.printer_HP_Officejet_6500_E709n_Series.print_edge_top	0
print.printer_HP_Officejet_6500_E709n_Series.print_evenpages	true
print.printer_HP_Officejet_6500_E709n_Series.print_footercenter	
print.printer_HP_Officejet_6500_E709n_Series.print_footerleft	&PT
print.printer_HP_Officejet_6500_E709n_Series.print_footerright	&D
print.printer_HP_Officejet_6500_E709n_Series.print_headercenter	
print.printer_HP_Officejet_6500_E709n_Series.print_headerleft	&T
print.printer_HP_Officejet_6500_E709n_Series.print_headerright	&U
print.printer_HP_Officejet_6500_E709n_Series.print_in_color	true
print.printer_HP_Officejet_6500_E709n_Series.print_margin_bottom	0.5
print.printer_HP_Officejet_6500_E709n_Series.print_margin_left	0.5
print.printer_HP_Officejet_6500_E709n_Series.print_margin_right	0.5
print.printer_HP_Officejet_6500_E709n_Series.print_margin_top	0.5
print.printer_HP_Officejet_6500_E709n_Series.print_oddpages	true
print.printer_HP_Officejet_6500_E709n_Series.print_orientation	0
print.printer_HP_Officejet_6500_E709n_Series.print_page_delay	50
print.printer_HP_Officejet_6500_E709n_Series.print_paper_data	1
print.printer_HP_Officejet_6500_E709n_Series.print_paper_height	11.00
print.printer_HP_Officejet_6500_E709n_Series.print_paper_name	
print.printer_HP_Officejet_6500_E709n_Series.print_paper_size_type	0
print.printer_HP_Officejet_6500_E709n_Series.print_paper_size_unit	0
print.printer_HP_Officejet_6500_E709n_Series.print_paper_width	8.50
print.printer_HP_Officejet_6500_E709n_Series.print_plex_name	
print.printer_HP_Officejet_6500_E709n_Series.print_resolution	0
print.printer_HP_Officejet_6500_E709n_Series.print_resolution_name	
print.printer_HP_Officejet_6500_E709n_Series.print_reversed	false
print.printer_HP_Officejet_6500_E709n_Series.print_scaling	1.00
print.printer_HP_Officejet_6500_E709n_Series.print_shrink_to_fit	true
print.printer_HP_Officejet_6500_E709n_Series.print_to_file	false
print.printer_HP_Officejet_6500_E709n_Series.print_unwriteable_margin_bottom	0
print.printer_HP_Officejet_6500_E709n_Series.print_unwriteable_margin_left	0
print.printer_HP_Officejet_6500_E709n_Series.print_unwriteable_margin_right	0
print.printer_HP_Officejet_6500_E709n_Series.print_unwriteable_margin_top	0
privacy.sanitize.migrateFx3Prefs	true
storage.vacuum.last.index	1
storage.vacuum.last.places.sqlite	1390059615
Graphics
Adapter Description	ATI Radeon HD 5450
Adapter Drivers	aticfx64 aticfx64 aticfx64 aticfx32 aticfx32 aticfx32 atiumd64 atidxx64 atidxx64 atiumdag atidxx32 atidxx32 atiumdva atiumd6a atitmm64
Adapter RAM	512
Device ID	0x68f9
DirectWrite Enabled	false (6.2.9200.16571)
Driver Date	2-8-2011
Driver Version	8.822.0.0
GPU #2 Active	false
GPU Accelerated Windows	1/1 Direct3D 9
Vendor ID	0x1002
WebGL Renderer	Google Inc. -- ANGLE (ATI Radeon HD 5450 Direct3D9Ex vs_3_0 ps_3_0)
windowLayerManagerRemote	false
AzureCanvasBackend	skia
AzureContentBackend	none
AzureFallbackCanvasBackend	cairo
AzureSkiaAccelerated	0
JavaScript
Incremental GC 	true
Accessibility
Activated 	false
Prevent Accessibility 	0
Library Versions
	Expected minimum version	Version in use
NSPR	4.10.2	4.10.2
NSS	3.15.3.1 Basic ECC	3.15.3.1 Basic ECC
NSSSMIME	3.15.3.1 Basic ECC	3.15.3.1 Basic ECC
NSSSSL	3.15.3.1 Basic ECC	3.15.3.1 Basic ECC
NSSUTIL	3.15.3.1	3.15.3.1

BERMEA:

    You responded:  Bj258: 

Do you get any error message when trying to play videos? Can you post a screenshot? Please see How do I create a screenshot of my problem?

Once you've done this, attach the saved screenshot file to your forum post by clicking the Browse... button below the Post your reply box. This will help us to visualize the problem.

   I did not get an error message.  When I click on the url in an email I go to the respective video but all I get is a blank video screen.  The cursor quickly flashes like something is loading but the video does not appear.

First thing that comes to mind is one of your extensions, particularly GreatArcadeHits. Upon doing a search on it, I came across this from botcrawl.com:

The GreatArcadeHits virus (also found as the Great Arcade Hits virus; though not technically a computer virus) is a potentially unwanted program or combination of potential malware, categorized as adware, browser hijacker, and spyware that primarily installs to computer systems with or without consent alongside software downloaded from download.com and other monetized freeware and shareware distribution websites.

So you will want to definitely uninstall that from your extensions. Go to Firefox button/File>Add-Ons/Extensions then uninstall GreatArcadeHits.

Also, go to your Control Panel, XP Instructions: Start>Control Panel>Classic View>Add/Remove Programs and check to see if GreatArcadeHits is there. If it is, uninstall it.

One last thing, you will want to scan your computer for viruses. You can try these free programs to scan for malware, which work with your existing antivirus software:

• Microsoft Safety Scanner
• MalwareBytes' Anti-Malware
• TDSSKiller - AntiRootkit Utility
• Hitman Pro
• ESET Online Scanner

Microsoft Security Essentials is a good permanent antivirus for Windows 7/Vista/XP if you don't already have one.

Further information can be found in the Troubleshoot Firefox issues caused by malware article.

Did this fix your problems? Please report back to us!

as a workaround on youtube you could enable the html5-player which doesn't depend on flash or any external plugins to playback video content: www.youtube.com/html5

edit: i think the Default Manager extension is malicious too. maybe also run a scan with adwcleaner, which is specialised in browser hijackers and adware.

As you recommended I uninstalled GreatArcadeHits. It worked. Thank you.

While I have you attention I have another question. Everytime open Mozilla Firefox I get a pop up titled USER ACCESS CONTROL which asks "Do you want to allow the following program to make changes to this computer". Why am I getting this pop up? Is it necessary? If not, how do I turn it off. Whereas I do not want changes/updates to my computer without my approval I just don't understand why I get the pop up ever time I open up FIREFOX.

Thank you Bj258

Great! Glad you got that fixed!

The user access control prompt is a safety precaution by Windows asking you if you want to allow Firefox to run.

You can disable it for the entire system, but that puts you at risk from unknown source files. I suggest keeping it on but if you want me to tell you how to disable that for Firefox I will. You are probably running Firefox as an administrator every time. Right click the Firefox shortcut on your desktop, click Properties then click the Advanced button near the bottom in the window that pops up, then uncheck the Run as Administrator box, press OK twice and you're done!

Does that work for you?

One question. What operating system are you running? Your troubleshooting info say 5.1 which is XP, and you are saying that User Access Control is notifying you of this. UAC is only available from Vista onward, not on XP.

Can you clarify what OS you are running?

This error is usually caused because Firefox is set to run as Administrator.

Check that Firefox isn't set to run as Administrator.

Right-click the Firefox desktop shortcut and choose "Properties".

Make sure that all items are deselected in the "Compatibility" tab of the Properties window.

• Privilege Level: "Run this program as Administrator" should not be selected
• "Run this program in compatibility mode for:" should not be selected

Also check the Properties of the firefox.exe program in the Firefox program folder (C:\Program Files\Mozilla Firefox\).

1. I found the "Run this program as Administrator" by right clicking on the desktop FIREFOX icon, then Properties, then the Security tab, then advanced but the "Run this program as Administrator" box was not checked.

2. I am running windows 7 version pack 1.

Did you check the Properties of the Firefox.exe program in the Firefox program folder as well?

Problem solved. I went to Mozilla FIREFOX properties/compatability. There I found the box for "Run this Program in Compatability Mode" was checked. It was for Windows XP (Service Pack 5). I unchecked the box and all seems to be well.

thanks to all for your help.  :-)