Not able to secure website on Firefox even after installing SSL certificate - node.js

Question

I am using the below code to install SSL certificate on my website:
const express = require('express');
const path = require('path');
const app = express();
const fs= require('fs');
let privateKey = fs.readFileSync('certificate/x.key', 'utf8');
let ca = fs.readFileSync('certificate/x.crt', 'utf8');
let certificate = fs.readFileSync('certificate/x.crt', 'utf8');
let credentials = { key: privateKey, cert: certificate, ca: ca };
const http = require('http');
const https = require('https');
app.use(express.static(path.join(__dirname, 'build')));
app.get('/*', function(req, res) {
res.sendFile(path.join(__dirname, 'build', 'index.html'));
});
let httpsServer = https.createServer(credentials, app);
httpsServer.listen(443);
This is a react app and I am serving it via Node.js.
When I open the website on Chrome or Microsoft Edge, it shows the connection as secure, encrypted and valid but when I open it on firefox, it shows that the connection is not secure.
What could be the problem?

Answer 1

If your intermediate certificate contains multiple blocks, then you should split them into different files and send them one-by-one as an array in ca parameter like this:
let credentials = { key: privateKey, cert: certificate, ca: [
fs.readFileSync('certificate/x_1.pem', 'utf8'),
fs.readFileSync('certificate/x_2.pem', 'utf8'),
fs.readFileSync('certificate/x_3.pem', 'utf8'),
[...]
] };

Answer 2

If your certificate looks correct on other Browsers and simply does not appear in Firefox, the reason is almost certainly, that Firefox still shows a cached certificate.
Simply clear Firefox's SSL state and you should be good to go:
On the History menu, click Clear Recent History. The Clear All History dialog appears.
In the Time range to clear list box, select Everything.
Select the Active Logins check box.
Click Clear Now.
Source:
https://www.a2hosting.co.uk/kb/getting-started-guide/internet-and-networking/clearing-a-web-browsers-ssl-state#Mozilla-Firefox

Answer 3

I suggest you to enter your site address here and test it for issues.
If you see, e.g. full chain not provided issue, you can create a full chain of all your certificates and PEM-encode it into a single cert file, then provide it as a cert file. You can even download this full chain there directly after the test, too.
Providing a full chain fixed issues for me several times, where everything worked fine in chrome, but not in some other cases.