SUMMARY
When running the latest plasma desktop (using kdesrc-build), firefox does not launch. It gives the error Error: cannot open display: :0"

STEPS TO REPRODUCE
1. Follow the steps to install the latest kwin + plasma: https://community.kde.org/Get_Involved/development#Plasma
2. Log onto a new wayland session
3. Try to start firefox

OBSERVED RESULT
Error: Cannot open display: 0

strace snippet:
socket(AF_UNIX, SOCK_STREAM|SOCK_CLOEXEC, 0) = 4
connect(4, {sa_family=AF_UNIX, sun_path="/run/user/1000/:0"}, 20) = -1 ENOENT (No such file or directory)
close(4)                                = 0
write(2, "Error: cannot open display: :0\n", 31Error: cannot open display: :0
) = 31
gettid()                                = 121975



EXPECTED RESULT


SOFTWARE/OS VERSIONS
Windows: 
macOS: 
Linux/KDE Plasma: 
(available in About System)
KDE Plasma Version: 
KDE Frameworks Version: 
Qt Version: 

ADDITIONAL INFORMATION