Caused by a Bug in Firefox 3.0+ versions, related to certain font glyphs.
https://bugzilla.mozilla.org/show_bug.cgi?id=454532
(Please don't comment in that Bug report unless you can provide a patch to fix the problem.) https://bugzilla.mozilla.org/page.cgi?id=etiquette.html

You can avoid that sometimes by using Print Preview and then printing from the Preview window.

I see patches available there, are they actual fixes? If so, how do I go about applying them? Thanks.

Those patches are for testing only, in a special build compiled with that patch. You would need to compile or build your own version of Firefox that included that patch
https://bugzilla.mozilla.org/show_bug.cgi?id=454532#c63
and here
https://bugzilla.mozilla.org/show_bug.cgi?id=454532#c65
There were special builds available for a short time to test an earlier patch, problem is that the "special builds" availability elapses too quickly and I don't know if they get tested by enough users.

I have no knowledge of building a version of Firefox, that sounds extensive for an average internet user wanting to print some documents. Is there any other simpler way, or will I have to revert to another browser?

Until a successful patch is created, tested, and available in a release version of Firefox, you'll have to use a different browser for printing pages that cause that problem with Firefox.

You could install IE Tab 2 and have that page always be displayed in Firefox in an "IE Tab" and print from there.
https://addons.mozilla.org/en-US/firefox/addon/92382

This is much more feasible. I have it installed, and it seems to be a great fix for the issue. Thanks for your help.

You're welcome.

Please click the Helpful button next to the answer that solved your Firefox support issue, when you are logged in, so this thread gets marked as Solved to help other users who may have this same problem.