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.

Information on where to find your profile folder can be accessed here.

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