I have created NPAPI browser plugin. My plugin can handle certain mime-types, but i wish to give the user an option whether he wants to load the content using plugin or browser should take the default action. A Gtk dialog box with these options. But is it possible to give control back to browser after plugin is loaded.
There's no way to undo the handoff of content to a plugin, no.
Is this embedded content, or content loaded directly in its own tab? If it's the former, you could use JS to decide whether or not to create the plugin object in the first place. If it's the latter, and you control how the user gets to the content, you could give them a choice and then serve the content two different ways, one with the default type (which you wouldn't register your plugin for), and one with a special type your plugin handles.