Comment # 4 on bug 1227486 from Fabian Vogt

I still can't explain the behaviour you're observing.

> That happens when I click e.g. an URL mail in Thunderbird.

Can you clarify what you mean by "URL mail"? Do you mean clicking a link in a
mail that should open in firefox? In that case kmozillahelper should only check
which application to open the URL with but let TB handle the actual open
action.