Is there any plugin or setting for firefox that can simplify the invalid SSL certificate process to a single click, or even not put up any errors and just display a warning indicator?
Working on a dev network using self-signed cerificates for initial design means contantly having to go through the 5 step process to grant an exemption for a site, which is a real pain when swapping things around.
Talk to your sysadmin. They can setup a CA on your domain (assuming a Windows network here). Have the dev servers use certs from that internal CA, which will be trusted by all machines on the domain.
You can use this addon to change the certificate acceptance behavior in Firefox:
https://addons.mozilla.org/en-US/firefox/addon/6843
One thing you might want to consider doing is to simply self sign a wildcard certificate for use on your development network. Then install that wildcard cert on all the systems. Once you accept the certificate once it should be good everywhere.