Galeon neither allows the setting of the per-printer print_edge_<bottom|top|left|right> settings via the UI, nor does it install sensible defaults for these.  The default prefs.js file contains what is apparently an attempt to set these globally for all printers ("print.print_edge_bottom", etc.) but these are neither honored by the program, nor is the default value (4/100 in.) large enough to put headers and footers within the printable area of most printers.

If reasonable per-printer values (integer values of 25 to 40) are set by editing prefs.js and inserting values for print.printer_<name>.print_edge_<edge> then Galeon will honor these when printing, and the values can be edited using about:config but no such per-printer lines are available unless prefs.js is manually edited and they're inserted.

I've been using Galeon for a number of years, and have posted on this issue before, so this may be a "WON'T FIX", which is a pity.  Unless some way of setting these values on a per-printer basis is made available in the UI, or some reasonable default setting is configured in when a printer is made available, then the headers and footers checkboxes and values might as well be disabled since the won't print on most printers, being right at the edge of the paper.