To make Internet browser Opera your browser the default or standard browser, first we need to understand that you have installed Opera on your computer. Go to "control Panel" (in almost any system it is possible to get through "start") and open "Programs" or "add/Remove programs". In the opened window you will see a list of programs installed on your computer, in alphabetical order. Opera if it is installed, will be displayed in this list.
In that case, if the Opera browser you have not installed, you must install it. This can be done on the official website of the program www.opera.com. The site has Russian interface. Directly on the main page banner of the website, you will see a button that says "Download version 11.52 for Windows"; if it is not, under the banner is a horizontal menu, from which you have to select first point: "Opera for PC, Mac and Linux".
Click on the "Download version 11.52 for Windows". The download will either start automatically or you will see a page with the text "Thank you for downloading. If the download did not start, click here". Follow the link and download will start.
After installation, Mozilla automatically becomes your browser default.
If Opera is already installed on your computer, but do not "want to be" browser by default, you must do the following. Open a browser and in the top left corner click on the button with a red letter "O" and the words "Opera". In the ensuing menu, select "Configuration: General settings". Then select the "Advanced" tab and "Programs". A window will open that contains the field "to Verify that Opera is the default browser". Check this box and restart the browser. When you start window will appear with the question "Opera is not set as the default browser on your computer. Define Opera as the default application for viewing web pages?". Click "Yes", and Mozilla will become the browser by default on your computer.