Published at: Mar 14, 2022
Starting with Firefox 98 (Released in March 2022), the default behaviour in Firefox is to now display the Downloads panel every single time you save a file to your computer.
A lot of people - myself included - find this incredibly annoying, so here's how to stop the downloads pop-out window appearing every time you save a file.
In the address bar, type in about:config and press enter. You do not need to put in http:// or www or anything like that; simply put about:config and press the Enter key on your keyboard.

The browser.download.alwaysOpenPanel setting will be true, because this is Firefox's new default setting. This is the preference we're going to change to stop the downloads panel appearing every time.

Either double click anywhere on the browser.download.alwaysOpenPanel line, or click the  Toggle button to change it from true to false.
 Toggle button to change it from true to false.

Once you have finished fixing Firefox's settings, simply close the Advanced Preferences tab and continue browsing the internet with less distractions.

A lot of people have raised this as an issue on the Mozilla Developers forums and other online discussion sites, so hopefully this will be switched off by default in the future.
Here's how to change settings in Firefox.