I get a pop-up window that says "URL cannot load." What gives?

Question

At random, well known sites, I randomly get a pop-up window that says, "The URL is invalid and cannot be loaded." Firefox does load the site but I must click out of the pop-up to proceed.
What gives? I'm running Windows 7 on a new HP laptop

Answer 1

'''~ I HAD THE SAME PROBLEM WHEN TRYING TO WATCH NETFLIX MOVIES ONLINE SO I HAD TO SOURCE IT MYSELF BECAUSE NOONE ELSE HAD THE ANSWER, THESE ARE THE STEPS I TOOK: (MOZILLA FIREFOX 4)'''
'''1.''' MAKE SURE YOUR NETWORK SETTINGS ARE SET TO "AUTODETECT SETTINGS FOR THIS NETWORK", (TOOLS--> OPTIONS--> ADVANCED--> NETWORK--> CONNECTION SETTINGS--> "AUTODETECT PROXY SETTINGS FOR THIS NETWORK"
'''2.''' DISABLE ALL EXTENSIONS; (TOOLS--> ADDONS --> EXTENSIONS)
(I ALSO HAVE AVG ANTIVIRUS, SO I HAD TO DISABLE THE AVG TOOLBAR EXTENSION)
'''3.''' DISABLE MOST ADDONS EXCEPT ESSENTIALS LIKE SILVERLIGHT, SHOCKWAVE FLASH , & JAVA PLATFORM; (TOOLS--> ADDONS --> ADDONS)
'''''~ NOTE: IF YOU HAVE MORE THAN ONE AUDIO/VIDEO PLAYER THERE MAY BE A CONFLICT.'''''
'''4.''' IF YOU HAVE ITUNES IT WILL INSTALL QUICKTIME AS THE DEFAULT HANDLER OF APPLICATIONS IN YOUR BROWSER, SO I HAD TO UNINSTALL QUICKTIME WHICH I NEVER USE.
'''5.''' IF YOU HAVE REALPLAYER, IT MAY ALSO CAUSE CONFLICTS WITH YOUR ADDONS & OTHER AUDIO/VIDEO PROGRAMS, SO I UNINSTALLED IT SINCE I WAS ONLY USING IT TO RECORD & DOWNLOAD INTERNET VIDEOS (OPTING FOR A SIMPLER DOWNLOADER)
'''6'''. I FINALLY HAD NO PROBLEMS WITH INSTANT WATCHING OR URL INVALID PAGES ON NETFLIX, ETC., AFTER FOLLOWING THE PREVIOUS STEPS.
'' ''' GOOD LUCK'''''