Not sure why you unable to locate the path
Can you skip that step and proceed with next main step :
- Open the Registry Editor.
- Navigate to the HKEY_CURRENT_USER\SOFTWARE\Mozilla\NativeMessagingHosts\com.uipath.chromenativemsg key.
- Open the (Default) REG_SZ value. The Edit String window is displayed and should contain a path similar to C:\Users\YOUR_USER_NAME\AppData\Local\UiPath\uipath-ff.json.
- Open the .json file at the path found above with a text editor (Notepad).
If error still persist then please reset setting and uninstall the extension restart the system and install extension again.
PS: please try with Firefox 32 bit in case you have 64 bit.