Nodemailer form doesn’t work on the Firefox web browser

I was trying to implement a form that uses Next.js & Nodemailer to send emails, and it works just fine on Chrome & Bing. However, I am unable to send emails using Firefox.

This is the button that inputs the form data to the backend (in pages/index.js):

<input type="submit" onClick={onSubmit} disabled={!values.name || !values.subject || !values.email || !values.message} />

This is the function that is called onClick (in pages/index.js):

  const onSubmit = async () => {
    try {
      await sendContactForm(values);
    } catch (error) {
      console.log(error);
    }
  };

This is the function that awaits the form data (in lib/api.js):

export const sendContactForm = async (data) =>
  fetch("/api/contact", {
    method: "POST",
    body: JSON.stringify(data),
    headers: { "Content-Type": "application/json", Accept: "application/json" },
  }).then((res) => {
    if (!res.ok) throw new Error("Failed to send message");
    return res.json();
  });

This is the function that sends the email (the nodemailer configuration was done in a different file) (in pages/api/contact.js):

import { mailOptions, transporter } from "config/nodemailer.js";

const handler = async (req, res) => {
  if (req.method === "POST") {
    const data = req.body;
    if (!data || !data.name || !data.email || !data.subject || !data.message) {
      return res.status(400).send({ message: "Bad request" });
    }
    try {
      await transporter.sendMail({
        ...mailOptions,
        ...generateEmailContent(data), //This is a function that returns the user inputted form data as a string
        subject: data.subject,
      });
      return res.status(200).json({ success: true });
    } catch (err) {
      console.log(err);
      return res.status(400).json({ message: err.message });
    }
  }
  return res.status(400).json({ message: "Bad request" });
};

Here is the GitHub repository as well for more context: https://github.com/Jacques-Bisset/nodemailer-testing

Here are some things I tried in the Firefox settings:

• Disabled HTTPS-only mode
• Turned browser security mode to “standard” instead of “strict”
• Unmarked all checkboxes in the “Deceptive Content and Dangerous Software Protection” settings

None of these configurations seem to have done anything

As I said before, this code works perfectly fine in other web browsers – it is in Firefox specifically where no email is sent for whatever reason.

However, when I click the submit button on Firefox, this message pops up in the terminal:

warn  - Fast Refresh had to perform a full reload. Read more: https://nextjs.org/docs/messages/fast-refresh-reload

This also only occurs for Firefox and not other web browsers.

Thank you for any help in advance.