Getting url from active tab on external page - firefox-addon

Question

I have create a very simple addon for personal use. The only thing it does is show a "popup" with an external url. So far it works fine, but now I of course want to add features. For this I would like to access the url of the tab on which the extension is opened. I have tried many things, but I can't seem to put my finger on it. I would also be glad with the url being added as a parameter to the url of "default_popup".
This is my manifest.json:
{
"browser_action": {
"browser_style": true,
"default_title": "Name of addon",
"default_popup": "https://www.testdomain.com/dir/"
},
"icons": {
"48": "lock.svg",
"96": "lock.svg"
},
"description": "Open given page in window on top of browser I guess...?",
"manifest_version": 2,
"name": "Name of addon",
"version": "1.0.11",
"permissions": [
"tabs"
],
"applications": {
"gecko": {
"id": "name#testdomain.com"
}
}
}
It's probably just a simple thing for you seasoned developers, but I have only started today :)

Answer 1

You'll have to declare the popup to use a page that belongs to the extension. The script inside that page will be able to get the current tab's URL and redirect the popup to the external site.
manifest.json, inside browser_action section:
"default_popup": "popup.html"
Create popup.html:
<script src="popup.js"></script>
Create popup.js:
(async () => {
const [tab] = await browser.tabs.query({active: true, currentWindow: true});
location.href = 'https://www.example.com/?foo=' + encodeURIComponent(tab.url);
})();