Could you describe your request in more detail?

Are you referring to dragging selected text from a web page to Firefox's search bar on the right side of the Navigation toolbar?

What would you like to happen when you drag-and-drop that text?

I dragged selected text from a web page and released the mouse anywhere, then a new tab page appeared. The firefox (version 24) is running on windows 8.

Hmm, I haven't heard of that before. It's a new tab page with no relation to what you were dragging?

I wonder whether this might be a feature of one of your extensions. You can review them, and disable/remove any that are nonessential or unrecognized, here:

orange Firefox button (or Tools menu) > Add-ons > Extensions category

If you disable extensions, usually a link will appear above at least one of them to restart Firefox. You can complete your work on the tab and click one of the links as the last step.

If that makes no difference, you could test in Firefox's Safe Mode -- that's a standard diagnostic tool to bypass interference by extensions (and some custom settings). More info: Diagnose Firefox issues using Troubleshoot Mode.

You can restart Firefox in Safe Mode using

Help > Restart with Add-ons Disabled

In the dialog, click "Start in Safe Mode" (not Reset)

Any difference?

Thanks! It is fixed after removing an Extension.