There is a button named 'Fit to Width' in Opera. (I don't know maybe other browsers have something similar.) So, my question is how to make this button invalid while browsing my web site. I don't like this button because web design gets destroyed if this option is active.
For referece, the fit to width feature you describe is illustrated here.
Although the meticulous designer will hate this answer, you shouldn't disable this feature. Things on the user's interface outside of your page, including scrollbars, menus, and the rest of the web browser shouldn't be manipulated. A user could also break your web page layout with a user stylesheet, and those are similarly beyond a web designer's ability to alter.
The best option in this case is to make a page which can be resized horizontally without creating a horizontal scrollbar. If you do that, users will be less likely to use the feature in Opera, and your page will probably behave better when the feature is active.
To get you started, you can add the CSS styling overflow: auto;
to individual elements so they dynamically gain scrollbars as needed. I realize that it is very difficult to keep a design that looks good as well as resizes nicely. Perhaps you could submit questions about how to get particular elements on your page to resize elegantly...?