Symptoms

When attempting to use the Edit in Word feature of the Office Connector in FireFox, the following error appears:

FireFox could not install the file at
http://<your confluence url>/download.resources/com.atlassian.confluence.extra.officeconnector:viewfile/webdavloader.xpi
Not a valid install package -207

Cause

A custom theme or decorator is responsible for the installation failure. There is a bug report for this in Webdav Launcher Fails to Install in Firefox Due to 'Not a valid install package -207'.

Resolution

Switch to the Default Theme and try the installation again, from Browse >> Space Admin >> Themes. You must be a space administrator to access this page.