Firefox used to have some plugins that you could use to customize your command keys pretty easily, but as Firefox has evolved recently, many of the XUL generation of shortcut keys has been disabled.
It's very easy to rebuild Firefox to support the keys that you want though. First, you'll want to run once to build the initial "key-shortcuts.properties" file.
On Linux, the relative file path is:
obj-x86_64-pc-linux-gnu/dist/bin/browser/chrome/en-US/locale/en-US/devtools/startup/key-shortcuts.properties
Open key-shortcuts.properties, you'll find it in:
Then you'll want to change the default C shortcut key that conflicts with my terminal muscle memory of CTRL+C to interrupt, and Shift + Ctrl + C as Copy...
# LOCALIZATION NOTE (inspector.commandkey):
# Key pressed to open a toolbox with the inspector panel selected
inspector.commandkey=MThe full workflow is...
# Grab the friendly mozilla build bootstrapper
cd ~/SourceInstall
curl https://hg.mozilla.org/mozilla-central/raw-file/default/python/mozboot/bin/bootstrap.py -O
# Run the bootstrap script
python3 bootstrap.py
# Do a test build to make sure it works
./mach build
./mach run
# edit file you want to change
./mach build
./mach run
# test your shortcut now works...
cd ~/SourceInstall/mozilla-unified/obj-x86_64-pc-linux-gnu/dist/bin
# or link to anywhere else in your path that
# will have higher precedence than /usr/bin
sudo ln -s $HOME/SourceInstall/mozilla-unified/obj-x86_64-pc-linux-gnu/dist/bin/firefox /usr/local/bin/firefoxEnjoy beginning to really customize Firefox... Hopefully for you this is the beginning of more meaningful Firefox hacking than just editing a config file.