You can try and add /usr/bin to your $PATH environment variable which is not there right now for some reason. So instead of /usr/bin/rednotebook you can do:
export PATH="$PATH:/usr/bin"
rednotebook
To make this permanent you can set your $PATH permanently by editing your ~/.profile file. See:
$ rednotebook
Reading profile /etc/firejail/rednotebook.profile
Reading profile /etc/firejail/allow-python3.inc
Reading profile /etc/firejail/disable-common.inc
Reading profile /etc/firejail/disable-devel.inc
Reading profile /etc/firejail/disable-exec.inc
Reading profile /etc/firejail/disable-interpreters.inc
Reading profile /etc/firejail/disable-programs.inc
Reading profile /etc/firejail/disable-shell.inc
Reading profile /etc/firejail/whitelist-common.inc
Reading profile /etc/firejail/whitelist-runuser-common.inc
Reading profile /etc/firejail/whitelist-usr-share-common.inc
Reading profile /etc/firejail/whitelist-var-common.inc
Parent pid 2089986, child pid 2090005
25 programs installed in 70.47 ms
Warning: skipping alternatives for private /etc
Warning: skipping pango for private /etc
Private /etc installed in 36.68 ms
Private /usr/etc installed in 0.02 ms
Warning: cleaning all supplementary groups
Warning: cleaning all supplementary groups
Warning: /sbin directory link was not blacklisted
Warning: /usr/sbin directory link was not blacklisted
Blacklist violations are logged to syslog
Warning: cleaning all supplementary groups
Child process initialized in 626.40 ms
Cannot start application: No such file or directory
Parent is shutting down, bye…
so I disable firejail:
$ sudo firecfg --clean
$ rednotebook
bash: /usr/local/bin/rednotebook: No such file or directory
However if I disable firejail and open a new shell, it does work again when I just enter “rednotebook”