For a long time, I wondered why opening Jupyter notebooks through nbopen always led to XQuartz starting.  Now, I found the reason: nbopen uses webbrowser.py to open a web page, and webbrowser.py sees the `DISPLAY` variable being set and calls xdg-settings (which I installed via the xdg-utils port / MacPorts).

Apparently, in order to be able to fire up XQuartz on demand and to allow people starting X11 applications, `DISPLAY` is set to a string like `/private/tmp/com.apple.launchd.<somecode>/org.xquartz:0`.

I am using Safari and find this starting of XQuartz undesirable (causes a delay, uses system resources, leads to a new running program in the Dock / task switcher). On the other hand I can totally understand that the code makes sense.

As a workaround, I can unset DISPLAY, or uninstall xdg-utils (although it is useful, and may be a dependency of other ports), but I thought I should also bring it up here for discussion.

3.7 is a few years old and only gets security fixes.  Can you either test on current releases or whether code is still same?

The same code is present in trunk. 

I'm in favour of disabling usage of X11 browsers of macOS, that's almost certainly not what users want.

I no longer have XQuartz installed on my machine, but when I did I only used it for running X11 GUIs on remote Linux systems.

What I'm not entirely sure about: is this something we should back port or just apply to the trunk (3.10)? This is a behaviour change and as such I'd be inclined to only apply to trunk.

I was trying to be very honest, because I am still running 3.7 for production. However, I have carefully checked and the webbrowser.py has only seen (clearly) unrelated changes.

I've created a PR for this. 

Open question: Is this a bug fix (with back ports to 3.9 and 3.8) or a feature  (no back ports)?

webbrowser is 'generous' at to what browsers it will open, some of which are not what hardly anyone would want.  So I would call this an 'enhancement' (really 'disenchantment', like all removals;-) unless there were a technical reason other than those given for the exclusion.