Have Thunderbird 52 running in background

Just like what people asked here in the past (How to run Thunderbird in the background?, Start Thunderbird in background), I would like to have Thunderbird running at all times during which my PC is turned on and notify me of new e-mails.

In the past, many suggested FireTray, which is not available for Thunderbird >50.

What would be your best workaround?
I have Ubuntu 16.04/Thunderbird 52.

Related: Thunderbird 60.2.1 "MinimizeToTray revived" add-on stopped working

You can actually still use FireTray even though it's not officially supported for Thunderbird v52.

Open your web browser, go to the add-on's homepage, and download the add-on by clicking the "Download for Linux" button.

Then launch Thunderbird and open Add-ons Manager. Click on the button with a cogwheel, select "Install Add-on from File", and install FireTray from the downloaded file.

Alternatively, just launch Thunderbird and drag & drop the the downloaded file over the Thunderbird window to install the add-on.

Warning: Try this at your own risk. Since the FireTray project is discontinued you may get no support if it breaks something. (I'm using FireTray with Thunderbird 52 without any issue.)