I began today with such good intentions, but that wasn't to be. I got a few things done but the research I planned on doing I can no longer be bothered to do after resolving an unexpected issue.
After an update and a restart, I was confronted with this window:
After applying a few other remaining system updates and giving the machine a restart it was still misbehaving. Running it in safe mode from terminal seemed to be the only instance in which it started in an useable state, leading me to believe it must have been an add-on causing the issue.
Perhaps I should have spent a little more time trying to troubleshoot which add-on was causing me the issue but refreshing the installation seemed to be the easiest option, especially for a Sunday afternoon.
Which leads us here, Firefox working again, add-ons back in place and all of my custom block lists re-imported from a private gist once more. Time to chill out and watch a film on Netflix.