Use relative path in Firefox extension - firefox

Question

I develop Firefox extension with bundled executable file which should be run on browser startup.
To run process I need get nsIFile or nsILocalFile instance which points to executable file.
I know one solution how to get it using directory service:
var file = Components.classes["#mozilla.org/file/directory_service;1"].getService(Components.interfaces.nsIProperties).get("ProfD", Components.interfaces.nsIFile);
file.append("extensions");
file.append("<extension id>");
file.append("<relative path>");
But this solution has two disadvantages:
It doesn't work in development mode, when instead of installed extension I have only text file with real extension path
I'm not sure that it will work on all Firefox configurations because of hardcoded "extensions" part of the path
So is there any nicer way to run executable file which comes with Firefox extension?
Thanks.

Answer 1

You are making way too many assumptions about the directory structure of the Firefox profile - don't. The Add-on Manager API lets you get the path of a file inside the extension, you should use it:
Components.utils.import("resource://gre/modules/AddonManager.jsm");
AddonManager.getAddonByID("<extension id>", function(addon)
{
var uri = addon.getResourceURI("<relative path>");
var file = uri.QueryInterface(Components.interfaces.nsIFileURL).file;
...
});

Answer 2

A restartless addon's startup function (in the bootstrap.js file) will receive, as its first parameter, the path where the addon is installed. You can then play various tricks to read files inside the .jar file, if any: see https://github.com/protz/GMail-Conversation-View/blob/master/bootstrap.js#L55 as an example.
In a non-restartless case, I must confess I don't have much of an idea :).

Answer 3

I found this thread looking for a way to reference a path to an image hosted in extension's directory from a content script. Here's a solution:
Include your files in web_accessible_resources in the extension's manifest.
"web_accessible_resources": [
"images/*"
]
Absolute paths to these resources contain randomly generated UUID, therefore we're using runtime.getUrl() giving it the path relative to manifest.json. Example:
let myImg = document.createElement('img');
myImg.src = browser.runtime.getURL("images/my-img.png")