Proof-of-Concept Firefox Add-On to Redirect Before Page Loads

manifest.json

{
    "description": "Redirect AMP addresses to their non-AMP sources",
    "manifest_version": 2,
    "name": "AMP Redirect",
    "version": "0.1",
    "author": "Ultrabenosaurus",

    "_comments_": {
        "signed_xpi": "https://drive.google.com/file/d/1Pg19uXregtxfENnKO3tcvR2SiTu01IYf/view?usp=sharing",
        "source:": "https://gist.github.com/Ultrabenosaurus/b94d373f3a32d2b5d6ae5256e04784a7",
        "based_on": "https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/API/webRequest/onBeforeRequest",
        "userscript": "https://greasyfork.org/en/scripts/400161-amp-redirect"
    },

    "permissions": [
        "webRequest",
        "webRequestBlocking",
        "<all_urls>"
    ],

    "background": {
        "scripts": ["redirect.js"]
    }
}

redirect.js

/**
*
* name         AMP Redirect
* namespace    ultrabenosaurus.AMP
* version      0.1
* description  Redirect AMP addresses to their non-AMP sources
* author       Ultrabenosaurus
* signed XPI   https://drive.google.com/file/d/1Pg19uXregtxfENnKO3tcvR2SiTu01IYf/view?usp=sharing
* source       https://gist.github.com/Ultrabenosaurus/b94d373f3a32d2b5d6ae5256e04784a7
* userscript   https://greasyfork.org/en/scripts/400161-amp-redirect
*
* Based on MDN web docs: https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/API/webRequest/onBeforeRequest
*
* from: https://www-techradar-com.cdn.ampproject.org/v/s/www.techradar.com/amp/news/eliminating-vpns-for-more-secure-productive-remote-work?amp_js_v=a3&amp_gsa=1&usqp=mq331AQFKAGwASA%3D#referrer=https%3A%2F%2Fwww.google.com&amp_tf=From%20%251%24s
* to: https://www.techradar.com/news/eliminating-vpns-for-more-secure-productive-remote-work
*
*/

function UBredirect(requestDetails){
    // console.log(requestDetails);
    var a = requestDetails.url.split("/");
    // console.log(a);
    var al = a.length;
    var d = a[2].split(".")[0].replace(/-/g,".");
    // console.log(d);
    if(d == a[5]){
        var p = a[al-1].split("?")[0];
        for (var i = al-2; i > 6; i--) {
            if(a[i] !== "amp") { p = a[i]+"/"+p; }
            // console.log(a[i]);
        }
        // console.log(p);
        var s = a[0]+"//"+d+"/"+p;
        // console.log(s);
        return {
            redirectUrl: s
        };
    }
}

browser.webRequest.onBeforeRequest.addListener(
    UBredirect,
    {urls: ["<all_urls>"]},
    ["blocking"]
);

Re: https://addons.mozilla.org/en-US/firefox/addon/amp2html/reviews/1519663/

This is exactly what "Redirect AMP to HTML" is doing - source.

Yet on many pages there is no way to detect amp from the URL. On these pages page source (canonical link) must be checked.

If that was exactly what the add-on was doing, why was it not redirecting me for the example URL I have included in the comment block in the JS file? This code works perfectly and redirects such URLs, while that add-on does not.

Also, neither of the source links in your comment work for me:

why was it not redirecting me for the example URL I have included in the comment block in the JS file?

https://www-techradar-com.cdn.ampproject.org/v/s/www.techradar.com/amp/news/eliminating-...?

These are supported:

        'https://www.bing.com/amp/*',
        'https://www.google.com/amp/*'

        'https://cdn.ampproject.org/c/*',
        'https://*.cdn.ampproject.org/c/*',
        'https://bing-amp.com/c/*',
        'https://*.bing-amp.com/c/*'

        '*://t.co/*?amp=1'

You should probably report few samples to the author - maybe he will add them.

Also, neither of the source links in your comment work for me:

Hmmm, seems you have network issues. Works for me on two different browsers and two devices.