Thanks to Kurt Poulsen for making me aware of this one.
There is an error in the chrome.manifest file. I told Wizz RSS to use cs-CZ twice. So if your Danish looks a bit like Czech, here’s how to fix it.
1. Close Firefox.
2. Find the chrome.manifest file. On a windows PC it’ll be in C:Documents and SettingsusernameApplication DataMozillaFirefoxProfilessome-weird-number.defaultextensions{D5EDC062-A372-4936-B782-BD611DD18D86}
3. Open the chrome.manifest file using a text editor.
4. Find the line that reads – locale wizzrss da-DK jar:chrome/wizzrss.jar!/locale/cs-CZ/
5. Change the cs-CZ to da-DK and save the chrome.manifest file.
6. Restart Firefox.