I was surprised and felt deluded to find out that Fraidycat is an online service and that all its interface, user’s data and settings are transferred and function on the addon’s website (fraidyc.at) and not on the addon’s local address (moz-extension://…)

That fact should be mentioned, ideally in the first place, in the mozilla’s addon’s page and description,

even if there are the performance issues which the author quotes in the issue #210 of the addon’s support page, which I also afterwards read.