How can I stop Firefox from opening (to "File Not Found") when opening my Opera browser?

Question

Ever since I installed Opera 10.61 on my new computer (Windows 7 Ultimate operating system), whenever I open Opera, Firefox opens one second later with the following error message:
'''File not found '''
Firefox can't find the file at /C:/Users/Nasheed/AppData/Local/Opera/Opera/temporary_downloads/client-en.xml.
* Check the file name for capitalization or other typing errors.
* Check to see if the file was moved, renamed or deleted.
TRY AGAIN.
<nowiki>****************************************************</nowiki><br />
This happens EVERY TIME I OPEN THE OPERA BROWSER. How can I stop this from happening? I'm stumped.
[EXTRA INFO - I was unable to enable Firefox to access my previous profile on the new computer (despite putting the old profile in the appropriate Mozilla Firefox folder. So, there are now two profiles in that location.
After reading the answer to another forum member's question, I attempted to resolve the problem using Profile Manager, but I was unable to locate the Profile Manager. The Windows "Search" feature is not enabled on my new computer (nor can it be enabled from the Customize Start Menu options).]

Answer 1

Thank you for your response, Cor-el.
I had Opera set as my default browser since this began happening. I changed my default browser back to Firefox mainly because having Firefox open one or two seconds every time I open Opera was/is such a nuisance.
I believe this problem began because I attempted to manually transfer the files from my old computer to the new one (via the backed up files in my external drive). I was unfamiliar with Windows 7 when I did this. Microsoft changed the file set up from what I had been used to in Windows XP. I used XP for six years before being exposed to Windows 7 (I never had Vista).
I'm almost sure this problem has something to do with where I placed the application data when I was trying to reestablish the program set up on the new computer.