No, you can only disable that feature for all sites.

You can set the pref dom.successive_dialog_time_limit to 0 on the about:config page to remove that checkbox.

To open the about:config page, type about:config in the location (address) bar and press the "Enter" key, just like you type the url of a website to open a website.
If you see a warning then you can confirm that you want to access that page.

• Use the Filter bar at to top of the about:config page to locate a preference more easily.
• Preferences that have been modified show as bold (user set).
• Preferences can be reset to the default or changed via the right-click context menu.

Большое спасибо. Помогло. А есть ли полное описание параметров about:config ?

http://kb.mozillazine.org/About:config_entries Be careful when editing about:config entries.

You're welcome.

There are also comments in these files (open the links to those files via the location bar):

• resource:///greprefs.js
• resource:///defaults/pref/firefox.js

А у меня нет такой настройки((( Firefox 7, win XP