quasicomputational/background.js

## background.js
browser.browserAction.onClicked.addListener(() => {
    browser.tabs.query({ active: true })
        .then((tabs) => {
            for (tab of tabs) {
                browser.tabs.update(tab.id, { url: "/test.html" });
            }
        });
});

## manifest.json
{ "manifest_version": 2
, "name": "Test"
, "version": "1.0"
, "browser_action":
  { "browser_style": true
  , "default_icon": "icon.svg"
  }
, "background":
  { "scripts": ["background.js"]
  }
, "permissions":
  [ "activeTab"
  ]
}

## test.html
<!DOCTYPE html>
<script src=test.js></script>

## test.js
window.location.replace("https://example.com");
	browser.browserAction.onClicked.addListener(() => {
	browser.tabs.query({ active: true })
	.then((tabs) => {
	for (tab of tabs) {
	browser.tabs.update(tab.id, { url: "/test.html" });
	}
	});
	});
	{ "manifest_version": 2
	, "name": "Test"
	, "version": "1.0"
	, "browser_action":
	{ "browser_style": true
	, "default_icon": "icon.svg"
	}
	, "background":
	{ "scripts": ["background.js"]
	}
	, "permissions":
	[ "activeTab"
	]
	}