The category “holiday” in “themes” is incorrectly translated as “Urlaub”, which means “vacation” in American English (probably because “holiday” has that meaning in British English). It should read “Festtage” instead. Also, “Bewertungen von Firefox Add-ons” might be better than “Bewertungen zu Firefox-Add-ons” (although the original is not misleading). Sorry, if this is the wrong place to report such problems.
Unfortunately this is not the best place to report bugs/error involving localization, as there’s no guarantee that localizers responsible for that language will see them.
With that said, you say “Mozilla site”, but there are a lot of Mozilla websites. Where did you see these exactly (URL)?
You can report bugs on Bugzilla, and use this link for German, but please provide details on where you saw that text.