After an OS crash files within the Firefox profile folder might be corrupt and lead to non-functional websites (in my case ironically the Firefox marketplace). Here, webappsstore.sqlite was affected.
As user @Oli stated over at Ask Ubuntu
Firefox stores its HTML5 data in a file called webappsstore.sqlite.
That’s sitting in your profile directory which lurks somewhere in
~/.mozilla/firefox/….default/ (depending on what your profile is
called).Move that out the way and restart Firefox and everything will come
back to life.
More: https://developer.mozilla.org/en/dom/storage
If deleted/moved out of your profile folder, Firefox builds a new, sanitized webappsstore.sqlite file. Worked for me.
Information on where to find your profile folder can be accessed here.