Toggle javascript support programmatically without restarting firefox

The problem: toggle javascript support without restarting firefox (nor resorting to different driver) during cucumber test run.

If Firefox's prefutils were exposed to javascript in a web page, that would make it possible. But it is not the case.

So, is there a plugin that does it? Or is there another way to solve the problem? Or is there a good tutorial (that highlights the exposing bit) on how to make such a plugin?

Edit

On a second thought, how would j开发者_Go百科avascript be of any help once it is disabled? Probably the whole idea is a bit screwed.

I assume that your tests run with normal web content privileges. In that case, they aren't going to be able to affect browser settings such as whether JavaScript is enabled (I assume that's what you mean by "toggle JavaScript support").

I'd implement a simple XPCOM component with a method to turn JS support on and off (by setting the appropriate pref). You can expose it as a JavaScript global property so that your tests can access it. See Expose an XPCOM component to javascript in a web page for more details. Package your component in an extension and make sure it is installed in the Firefox instance where your tests are running.

If you want to access the preferences API directly from your content script, you can add the following prefs to Firefox, either in about:config or by adding the following lines to prefs.js in your profile directory:

user_pref("capability.principal.codebase.p1.granted", "UniversalXPConnect UniversalBrowserRead UniversalBrowserWrite UniversalPreferencesRead UniversalPreferencesWrite UniversalFileRead");
user_pref("capability.principal.codebase.p1.id", "http://www.example.com");
user_pref("capability.principal.codebase.p1.subjectName", "");`
user_pref("signed.applets.codebase_principal_support", true);

Replace www.example.com with the domain that you want to grant the privileges to. Also add this line to your JS code before you call the preferences API:

netscape.security.PrivilegeManager.enablePrivilege('UniversalXPConnect');

A local file (something loaded from file:///) is allowed to request additional privileges. Normally you would get a prompt asking whether you want to allow access - you can "auto-accept" the prompt by adding the following lines to prefs.js in the Firefox profile:

user_pref("capability.principal.codebase.p0.granted", "UniversalXPConnect");
user_pref("capability.principal.codebase.p0.id", "file://");
user_pref("capability.principal.codebase.p0.subjectName", "");

You page can then do:

netscape.security.PrivilegeManager.enablePrivilege("UniversalXPConnect");
var branch = Components.classes["@mozilla.org/preferences-service;1"]
                       .getService(Components.interfaces.nsIPrefBranch);
branch.setBoolPref("javascript.enabled", false);

This will definitely work if your page is a local file. Judging by the error message however, you are currently running code from about:blank. It might be that changing capability.principal.codebase.p0.id into about:blank or into moz-safe-about:blank will allow that page to get extended privileges as well but I am not sure.

However, none of this will really help if JavaScript is already disabled and you need to enable it. This can only be solved by writing an extension and adding it to the test profile. JavaScript in Firefox extensions works regardless of this setting.

That means you need Javascript to toggle enabling or disabling Javascript.

function setJavascriptPref(bool) {
   prefs = Components.classes["@mozilla.org/preferences-service;1"]
           .getService(Components.interfaces.nsIPrefBranch);
   prefs.setBoolPref("javascript.enabled", bool);
}