Despite the /usr/local/share/doc/pkg-readmes/firefox-esr indications :
pledge(2) and unveil(2) Support
===============================
Firefox on OpenBSD is secured with pledge(2) and unveil(2) to limit
the system calls and filesystem access that each of Firefox's process
types
(main, content, remote data decoder, audio decoder, socket and GPU) is
permitted. By default, only ~/Downloads and /tmp can be written to when
downloading files, or when viewing local files as file:// URLs. You can
edit
the following files to change the pledge promises, unveil paths, and
associated
permissions:
/etc/firefox-esr/{unveil,pledge}.{content,gpu,main,rdd,socket,utility}
As unveil() can't show non-existing dirs, it is recommended to manually
create ~/Downloads for files to be properly saved in this directory.
Starting firefox-esr should create this directory, but it won't be
available
for downloads until it's restarted.
and default /etc/firefox-esr/unveil.main containing
~/.mozilla rwc
~/Downloads rwc
and default /etc/firefox-esr/unveil.content containing
~/.mozilla r
~/Downloads r
I cannot save downloads in ~/Downloads
Besides, I would like to access some of my local files, but can't manage
to find the right settings.