Trying uninstalling the Opera browser:

Settings>Applications>Manage applications

and then reinstalling it.

Alternatively download a new web browser eg Dolphin & once that is installed,launch your video & it should give you the option of selecting Opera as your default.

https://play.google.com/store/apps/details?id=mobi.mgeek.TunnyBrowser&hl=en

Trying uninstalling the Opera browser:

 Settings > Applications > Manage applications

and then reinstalling it.

Alternatively download a new web browser (e.g., Dolphin) and once that is installed, launch your video and it should give you the option of selecting Opera as your default.