See http://www.TiddlyTools.com/#CoreTweaks for a possible 'fixup' for FireFox?...

• The FF3 "type=file" "browse" control no longer provides access to the full path/filename of the selected file. This was done deliberately by the mozilla team, as part of a 'security improvement'.
• Unfortunately, TW still needs a way to ask for a *complete* path/file in order to properly request a local file for import, sync, etc.
• To provide TW with the information it needs when using FF3 (or any version of FireFox? for that matter), we can replace the use of the standard "browse" with a combination of text input+button controls that, when pressed, uses browser-secured filesystem I/O.
• The actual code tweak involves replacing the HTML that defines the standard file control used by backstage>import, so that, when FireFox? is used, an alternative fragment of HTML is used to render a secured text+button combination instead, which then re-enables access to the complete path+filename

Note: There is also the possibility of providing a similar solution for IE, so that it can be more secure as well.