Comment 5 for bug 1835024

I could reproduce this problem using 18.04.3 live CD using Slack and Atom. However, I don't think the problem is caused by snapd.

Slack, Skype and Atom are all classic snaps so they have full access to the system. With Slack installed, clicking on the 'get started' link was enough to get another Firefox window open. I collected the strace log. A relevant piece is here:

10782 execve("/usr/local/sbin/xdg-open", ["xdg-open", "https://slack.com/ssb/add"], 0xb6c9467b000 /* 75 vars */) = -1 ENOENT (No such file or directory)
10782 execve("/usr/local/bin/xdg-open", ["xdg-open", "https://slack.com/ssb/add"], 0xb6c9467b000 /* 75 vars */) = -1 ENOENT (No such file or directory)
10782 execve("/usr/sbin/xdg-open", ["xdg-open", "https://slack.com/ssb/add"], 0xb6c9467b000 /* 75 vars */) = -1 ENOENT (No such file or directory)
10782 execve("/usr/bin/xdg-open", ["xdg-open", "https://slack.com/ssb/add"], 0xb6c9467b000 /* 75 vars */) = 0
10784 execve("/usr/bin/which", ["which", "gnome-default-applications-prope"...], 0x560d5fb594a8 /* 75 vars */) = 0
10784 +++ exited with 1 +++
10782 --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=10784, si_uid=999, si_status=1, si_utime=0, si_stime=0} ---
10785 execve("/usr/bin/gio", ["gio", "help", "open"], 0x560d5fb594a8 /* 75 vars */) = 0
10785 +++ exited with 0 +++
10782 --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=10785, si_uid=999, si_status=0, si_utime=0, si_stime=0} ---
10786 execve("/usr/bin/gio", ["gio", "open", "https://slack.com/ssb/add"], 0x560d5fb594a8 /* 75 vars */) = 0
10789 +++ exited with 0 +++
10786 --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=10789, si_uid=999, si_status=0, si_utime=0, si_stime=0} ---
10790 execve("/usr/local/sbin/firefox", ["firefox", "https://slack.com/ssb/add"], 0x563485f1c6e0 /* 77 vars */) = -1 ENOENT (No such file or directory)
10790 execve("/usr/local/bin/firefox", ["firefox", "https://slack.com/ssb/add"], 0x563485f1c6e0 /* 77 vars */) = -1 ENOENT (No such file or directory)
10790 execve("/usr/sbin/firefox", ["firefox", "https://slack.com/ssb/add"], 0x563485f1c6e0 /* 77 vars */) = -1 ENOENT (No such file or directory)
10790 execve("/usr/bin/firefox", ["firefox", "https://slack.com/ssb/add"], 0x563485f1c6e0 /* 77 vars */) = 0
10791 +++ exited with 0 +++

Notice how slack attempts to run xdg-open (and does so successfully at some point), then it proceeds to run `gio open ..`, and again does that successfully, finally it just runs firefox with the URL. I believe this is what triggers the new window to appear.

Another observation for Slack on 18.04 is that gnome-shell groups the Firefox window *with* the slack one.

I tried diffing the environment between the inside and outside of snap:

--- in-shell 2019-10-17 13:43:59.474529198 +0000
+++ in-snap-shell 2019-10-17 13:44:09.186624002 +0000
@@ -2,13 +2,14 @@ CLUTTER_IM_MODULE=xim
 COLORTERM=truecolor
 DBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/999/bus
 DESKTOP_SESSION=ubuntu
+DISABLE_WAYLAND=1
 DISPLAY=:0
 GDMSESSION=ubuntu
 GJS_DEBUG_OUTPUT=stderr
 GJS_DEBUG_TOPICS=JS ERROR;JS LOG
 GNOME_DESKTOP_SESSION_ID=this-is-deprecated
 GNOME_SHELL_SESSION_MODE=ubuntu
-GNOME_TERMINAL_SCREEN=/org/gnome/Terminal/screen/113b5986_bfcc_47c1_8317_a37a7600b396
+GNOME_TERMINAL_SCREEN=/org/gnome/Terminal/screen/d399bea3_fa8f_4330_842a_0eaaac439533
 GNOME_TERMINAL_SERVICE=:1.143
 GPG_AGENT_INFO=/run/user/999/gnupg/S.gpg-agent:0:1
 GTK_IM_MODULE=ibus
@@ -27,7 +28,22 @@ QT_ACCESSIBILITY=1
 QT_IM_MODULE=ibus
 SESSION_MANAGER=local/ubuntu:@/tmp/.ICE-unix/4000,unix/ubuntu:/tmp/.ICE-unix/4000
 SHELL=/bin/bash
-SHLVL=1
+SHLVL=2
+SNAP_ARCH=amd64
+SNAP_COMMON=/var/snap/atom/common
+SNAP_CONTEXT=yBpkxSLRYnnStMxl74JWW8f6GLLQDXlD6qC2rdmXVjsh
+SNAP_COOKIE=yBpkxSLRYnnStMxl74JWW8f6GLLQDXlD6qC2rdmXVjsh
+SNAP_DATA=/var/snap/atom/238
+SNAP_INSTANCE_KEY=
+SNAP_INSTANCE_NAME=atom
+SNAP_LIBRARY_PATH=/var/lib/snapd/lib/gl:/var/lib/snapd/lib/gl32:/var/lib/snapd/void
+SNAP_NAME=atom
+SNAP_REEXEC=
+SNAP_REVISION=238
+SNAP=/snap/atom/238
+SNAP_USER_COMMON=/home/ubuntu/snap/atom/common
+SNAP_USER_DATA=/home/ubuntu/snap/atom/238
+SNAP_VERSION=1.40.1
 SSH_AGENT_PID=4095
 SSH_AUTH_SOCK=/run/user/999/keyring/ssh
 TERM=xterm-256color
@@ -43,7 +59,7 @@ XDG_CONFIG_DIRS=/etc/xdg/xdg-ubuntu:/etc
 XDG_CURRENT_DESKTOP=ubuntu:GNOME
 XDG_DATA_DIRS=/usr/share/ubuntu:/usr/local/share:/usr/share:/var/lib/snapd/desktop
 XDG_MENU_PREFIX=gnome-
-XDG_RUNTIME_DIR=/run/user/999
+XDG_RUNTIME_DIR=/run/user/999/snap.atom
 XDG_SEAT=seat0
 XDG_SESSION_DESKTOP=ubuntu
 XDG_SESSION_ID=2

However I could still spawn a separate Firefox window using a simple `gio open http://<url>`.

I've proceeded to install Chromium and set it to be my default browser. At this point all the links and xdg-open calls I tried would open a new tab in the current Chromium window.

Perhaps the problem is actually with Firefox and the method it uses to find out whether there's antoher instance already running.