Building firefox gives the following build dependencies:
pkgconfig(alsa) is needed by firefox-102.15.1-1.el9.x86_64
pkgconfig(dri) is needed by firefox-102.15.1-1.el9.x86_64
pkgconfig(gtk+-2.0) is needed by firefox-102.15.1-1.el9.x86_64
pkgconfig(gtk+-3.0) is needed by firefox-102.15.1-1.el9.x86_64
pkgconfig(krb5) is needed by firefox-102.15.1-1.el9.x86_64
pkgconfig(libcurl) is needed by firefox-102.15.1-1.el9.x86_64
pkgconfig(libnotify) >= 0.7.0 is needed by firefox-102.15.1-1.el9.x86_64
pkgconfig(libpulse) is needed by firefox-102.15.1-1.el9.x86_64
pkgconfig(libstartup-notification-1.0) is needed by firefox-102.15.1-1.el9.x86_64
pkgconfig(nspr) >= 4.34 is needed by firefox-102.15.1-1.el9.x86_64
pkgconfig(nss) >= 3.79 is needed by firefox-102.15.1-1.el9.x86_64
pkgconfig(pango) is needed by firefox-102.15.1-1.el9.x86_64
pkgconfig(xrender) is needed by firefox-102.15.1-1.el9.x86_64
pkgconfig(xt) is needed by firefox-102.15.1-1.el9.x86_64
pkgconfig(xtst) is needed by firefox-102.15.1-1.el9.x86_64
but I can find no package called pkgconfig in the Rocky repositories.
will both tell that feature āpkgconfig(nss)ā is provided by package nss-devel.
That feature is info for the build tools on how to include/link the nss library.
Obviously, the build tools do use some utility to read the info and that is the pkgconfig.
One could ask whether there is a file with that name in some package:
dnf provides */pkgconfig
but that output does not make us wiser.
One could ask whether such feature is provided by some packages:
Therefore, the installation of nss-devel (or probably any of the needed packages) will auto-install the āpgkconfigā too.
Why are you building Firefox? Rocky does provide one?
Are you building with rpmbuild?
The mock supposedly auto-installs those required packages (and does it in ācleanā chroot).
If you only want to browse code, you neither need to do a full build nor install any dependencies.
This is what I usually do, if I just want to look at the source of some package (As normal user - NOT as root):