fillForm.js

var query = window.location.search.substring(1);
var query = query.split("&");

for(i = 0; i < query.length; i++) {
  var split = query[i].split('=');
  var target = split[0];
  var value = split[1];

  if (target === "full_name") {
    var split_name = value.split('%20')
    var first_name = split_name[0];
    var last_name;

    for(k = 1; k < split_name.length; k++) {
      if(!last_name)
        last_name = split_name[k];
      else
        last_name = last_name + " " + split_name[k];
    }
    fillForm("first_name", first_name);
    fillForm("last_name", last_name);

  } else {
    fillForm(target, value);
  }

}


function fillForm(target, value) {
  value = decodeURIComponent(value);
  console.log(target, value);
  document.getElementById('id_' + target).value= value
}

manifest.json

{
  "manifest_version": "0.0.1",

  "name": "Homeloc auto fill form",
  "description": "This extensionA allows to autofill form fields from query parameter in the url",
  "version": "1.0",
  "content_scripts": [
    {
      "matches": ["https://www.homelocpay.com/fr/dashboard/payments/request/*"],
      "js": ["fillForm.js"]
    }
  ]
}