Interaction between PortableApps startup and non-Portable Firefox Bookmarks

Whenever I start or shut down the main PortableApps application using Start.exe (or a shortcut for it), a very odd behavior occurs...
I have Firefox installed on my computer as a non-portable app. It is up to date and runs without any issues I have seen. I do NOT have the portable version of Firefox installed as a PortableApp.
Any time Firefox is running, if I start the PortableApps menu, the Bookmarks sidebar in Firefox is collapsed and becomes non-responsive to input. I have to click the 'X' to close the sidebar and use Firefox's View | Sidebar | Bookmarks menu option to get back to a working Bookmarks menu.
This makes no sense to me and I can't find anything obvious that would cause it.
I've seen this behavior on both Win10 and Win11, on two different computers.
Any thoughts on how to track down the cause or prevent this would be greatly appreciated.
cheers,
Ron
p.s. I also noticed just now that when I directly run the Portable version of OpenOffice (e.g., open a spreadsheet), that this same behavior occurs. This does NOT happen when I directly run the Portable version of the Sumatra PDF reader.