What is Zen?

[PaulMcF1987]

I am just looking for a bit of clarification and mean no disrespect to the creator(s) of Zen

Is this a browser in its own right? Or, is it essentially a skin for Firefox

The reason I ask is...
When I look at the details of Arc on my desktop, the developer is, The Browser Company, when I sign in, I sign in to their site which syns everythig from their services, the same is true for sidekick

With Zen, however, when I view the details on my computer, the developer is Mozilla... When I sign in, I sign into my Mozilla profile. I uninstalled the browser so that I could start from scratch and it asked me to send feedback to Mozilla

So the other 2 I mentions, Arc and Sidekick, they appear to have taken the Chromium sourcecode and developed a standalone browser off the back of it

Is Zen the same? Or is this a "Skin" for the firefox browser which adds additional features and customisations?