New Browsers - HTML Files Changed, why?

Recently I installed Opera to see if I liked it. I didn't. I noticed that all the HTML files changed to Opera files. I uninstalled it and noticed that old HTML files had been changed to Opera files. What would cause this?

I did a system restore and the files are back to normal. Thank you!

 

Opera set itself to the system default browser, possibly setting other file-types it could handle as well. This is fine - if it offers this setting as a choice during install. Unfortunately, it looks like the uninstaller does not reference the Opera install log (if it created one) so that it could undo all changes made.

Ordinarily with modern Windows versions, resetting the default Program for file-types is reasonably painless, in W7, it's in Control Panel\All Control Panel Items\Default Programs.

 

Thanks satrow, I appreciate your help.

I forgot to add that my system is XP Pro. Thanks again.

 

With XP, I think you need to set the file associations individually from Control Panel.

 

You need to use your preferred browser and make it again the default browser.

Same problem happens with Chrome; after you uninstall it, it still remains the default browser.