Earlier quoted context omitted.
Did you not read the blog post? You can use the dev edition or the special release and beta version that don't have this limitation. Nobody is forcing you to live with this limitation. If this was done as an about:config flag it could easily be changed by an add-on too.
I did read the blog post. It says I have to use a less stable (beta) or less customizable (dev edition) version of Firefox to avoid this burden.
"What are my options if I want to install unsigned extensions in Firefox?
The Developer Edition and Nightly versions of Firefox will have a setting to disable signature checks. There will also be special unbranded versions of Release and Beta that will have this setting, so that add-on developers can work on their add-ons without having to sign every build."