Previously this error had been random between Appstacks and Writeable volumes, but now has become extremely consistent. The full message is something like:
C:\Program Files (x86)\Mozilla Firefox\firefox.exe
The device object parameter is either not a valid object or is not attached to the volume specified by the file name.
This will happen in a profile only (and UIA + profile) writable volume trying to download and install the application, or when UIA only is selected only when trying to run the installed applications. It's almost like the volume doesn't have read/write permissions, but other information, such as application related profile information is stored and used correctly.
Running version 2.9
Just a long shot here but it could be the Temp Google Chrome "bug".
What happens when you have a writable volume is that the disk is mounted into the operating system. If the writable volume doesn't have a drive letter it will see this disk as a network drive and say that it is unsafe and won't use it in any way. Maybe Firefox has the exact same issue.
You need the following registry key. What is does is give your writable volume a drive letter and hide it from the browser.
DWORD = DriveletterSetting=6
For testing purposes you could off course just assign a drive letter to your writable volume. Then you won't need to add this key and test it manually.