You have good tips in the Klassic Skin toolbars.cfg file:
#
# Toolbar Definition File for K-Meleon
#
# Jeff Doozan <jeff@tcbnetworks.com>
#
#
# ToolBar Name(16,16) { # (width, height) is optional, defaults to 16, 16
# Button Name(16, 16) { # (width, height) is optional, defaults to toolbar dimensions
# ID_NAV_STOP # command id (required)
# Stop Page Loading # Tooltip text
# c:\toolhot.bmp[2] # hot image (optional)
# # [2] (optional) is the zero based index of the
# # image within the file, defaults to 0
# c:\toolcold.bmp[2] # cold image (optional)
# c:\tooldead.bmp[2] # disabled image (optional)
# }
# }
#
# Notes:
# - If don't specify any images in the toolbar, it will become a "text" based
# toolbar, and use the button names in place of images
#
In green the toolbars, in blue the buttons (inside toolbars).
Of course,
make a backup of toolbars.cfg before edit it.