Firefox portable History not visible

I sync Firefox History between several PCs and one portable device.

The sync is working just fine but on the portable device I can't SEE the past history (just today's - from when you first click on "History").

So, when I go into "Show all History" there is nothing there. Though on the PC's I can see all the past history OK - including the activity on the portable device.

The problem seems to be peculiar to the portable version of Firefox.

Has anyone else noticed this or have a solution?

Thanks