I just tried allowing Firefox by sudo ufw allow Firefox. I get back the following message;

Traceback (most recent call last):
File "/usr/sbin/ufw", line 115, in <module>
pr.data['iptype'], pr.force)
File "/usr/lib/python3/dist-packages/ufw/frontend.py", line 679, in do_action
res = self.set_rule(rule, ip_version)
File "/usr/lib/python3/dist-packages/ufw/frontend.py", line 419, in set_rule
rules = self.backend.get_app_rules_from_template(rule)
File "/usr/lib/python3/dist-packages/ufw/backend.py", line 413, in get_app_rules_from_template
(port, proto) = ufw.util.parse_port_proto(p)
File "/usr/lib/python3/dist-packages/ufw/util.py", line 76, in parse_port_proto
raise ValueError
ValueError

Firefox's profile is in UFW's app list. I have tried other apps in the list with the same problem.
I did the same on another machine with no problem.
I did try uninstalling UFW and making sure that all UFW files were gone then reinstalling UFW.
Didn't work. Same message.
I know nothing about the files in the message so I have no idea what's wrong.
Using Ubuntu 14.04.

What are you looking to accomplish with that command?
And where did you get it?

shows me this:
See https://help.ubuntu.com/community/UFW and/or
https://help.ubuntu.com/community/Gufw

You have to have a profile for the app that you want to allow. Some make their own
UFW profiles but most you have to make one for them and put it in /etc/ufw/applications.d.
To show what applications are there, the command is> sudo ufw app list.
You will be presented with a list of app profiles that are stored.
The profile defines what port/s and what protocol/s the app can use.

Aren't the defaults enough?

That doesn't help me solve my problem.

If you are looking for hand-holding or to be spoon-fed, this is not the place for that.
I notice that you didn't answer the question. So, show us your firefox profile for UFW then.

If you don't know anything about app profiles in UFW then you obviously can't help.
Going beyond the defaults has nothing to do with why it won't work on this one computer.
I am not asking for hand holding. I am asking for some direction.
My Firefox UFW profile;

[Firefox]
title=browser
description=mail newsgroups
ports=80,443/tcp

Now tell me how this generates the print out I get from trying to allow Firefox.

You have no idea what I know or don't know.