How to add Content Security Policy to Firefox extension - firefox-addon

Question

I have a plugin which I have to support both on Chrome and Firefox browsers. The plugin does cross script loading.
In Chrome, by adding the content security policy in my manifest.json file, I could get away with it. How can I do it Firefox extension?

Answer 1

I couldn't find a simple solution for my problem and upon looking up some firefox plugin extensions i had to come up with my own solution as below. The below solution was tested on FF 24.0 but should work on other versions as well.
Cc["#mozilla.org/observer-service;1"].getService(Ci.nsIObserverService)
.addObserver(_httpExamineCallback, "http-on-examine-response", false);
function _httpExamineCallback(aSubject, aTopic, aData) {
var httpChannel = aSubject.QueryInterface(Ci.nsIHttpChannel);
if (httpChannel.responseStatus !== 200) {
return;
}
var cspRules;
var mycsp;
// thre is no clean way to check the presence of csp header. an exception
// will be thrown if it is not there.
// https://developer.mozilla.org/en-US/docs/XPCOM_Interface_Reference/nsIHttpChannel
try {
cspRules = httpChannel.getResponseHeader("Content-Security-Policy");
mycsp = _getCspAppendingMyHostDirective(cspRules);
httpChannel.setResponseHeader('Content-Security-Policy', mycsp, false);
} catch (e) {
try {
// Fallback mechanism support
cspRules = httpChannel.getResponseHeader("X-Content-Security-Policy");
mycsp = _getCspAppendingMyHostDirective(cspRules);
httpChannel.setResponseHeader('X-Content-Security-Policy', mycsp, false);
} catch (e) {
// no csp headers defined
return;
}
}
};
/**
* #var cspRules : content security policy
* For my requirement i have to append rule just to 'script-src' directive. But you can
* modify this function to your need.
*
*/
function _getCspAppendingMyHostDirective(cspRules) {
var rules = cspRules.split(';'),
scriptSrcDefined = false,
defaultSrcIndex = -1;
for (var ii = 0; ii < rules.length; ii++) {
if ( rules[ii].toLowerCase().indexOf('script-src') != -1 ) {
rules[ii] = rules[ii] + ' <My CSP Rule gets appended here>';
scriptSrcDefined = true;
}
if (rules[ii].toLowerCase().indexOf('default-src') != -1) {
defaultSrcIndex = ii;
}
}
// few publishers will put every thing in the default (default-src) directive,
// without defining script-src. We need to modify those as well.
if ((!scriptSrcDefined) && (defaultSrcIndex != -1)) {
rules[defaultSrcIndex] = rules[defaultSrcIndex] + ' <My CSP rule gets appended here>';
}
return rules.join(';');
};

Answer 2

There are plans in the future to add content policy natively in the SDK (bug 852297), but there is a 3rd party module that should get you close to where you want to be: policy.js