Can you replicate the error message yourself? For example, does it appear in Firefox's Error Console (Ctrl+Shift+j)? If you aren't getting user complaints about missing functionality, this might be a nonessential file, or it could be a spurious error related to the user's personal configuration (e.g., an add-on). There is a more global issue to watch for: During the past year Firefox started enforcing higher security restrictions for local web pages. Your page should be able to access files in the same folder or a subfolder. However, if the RoboHelp page is set up to access resources in a directory that requires navigation through a parent directory, that might be blocked. Hope this helps.