I am not a linux user, and not on my usual machine for accessing bookmarked items but look into Profile manager and articles about profiles eg: http://kb.mozillazine.org/Using_multiple_profiles_-_Firefox

Profiles aren't flexible enough for me, I'm afraid.

The profiles are what firefox uses for its data. There are command line options, also methods of creating profiles that do not display in the profile manager, as mentioned in the last article I linked to.

• See also: https://developer.mozilla.org/en/Command_Line_Options

Certainly I can work with multiple instances of firefox on a Windows machine.

I cannot put a profile on a flash stick, can I? Or in an encrypted container, can I? I can't use different plug-ins with different profiles, can I?

I'm NOT interested in profiles, please answer to the question as stated!

If you want to start Firefox with a profile at a specific location then you can add the full absolute path to the command line of the shortcut to start Firefox. Doing that on Linux shouldn't be a problem because Linux doesn't use drive letters that change.

See -profile "/path/to/profile"

• https://developer.mozilla.org/en/Command_Line_Options

I can't use different plug-ins with different profiles, can I? Yes , I often do.

"I cannot put a profile on a flash stick, can I?" Yes see answer above from cor-el