User Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:48.0) Gecko/20100101 Firefox/48.0 Build ID: 20160823121617 Steps to reproduce: Enter "Fahrgestellnummer" with German dictionary selected. Actual results: German Spell Checker suggest I meant "Fahrgenstellnummer", which is a typo inside the dictionary. Expected results: German Dictionary should contain the right word ("Fahrgestellnummer") and not suggest I change it.
Please note: Core::Spelling checker is for the en-US dictionary only. Since the German localisation doesn't ship with a dictionary, this is not a FF problem. See bug 1229454 comment #3. Maybe Kairo can look into it. BTW, the reporter doesn't even tell us which of the three available German dictionaries he's using.
I can confirm the wrong dictionary entry for this add-on: Wörterbuch Deutsch (de-DE), Hunspell-unterstützt, 20160829, by B. Jacke.
The dictionaries in my packages are just the ones that Björn Jacke has created, so it's him that this needs to be reported to.