Addon weirdness

I'm using FF 3.5.5 Portable, syncing it between two computers with a flash drive. When I transfer FF from one computer to another, I delete the previous Firefox folder - that could be important.
Anyway, some of my addons get screwed up. Several (CS Lite, JSView, ColorZilla, and a few others) don't correctly recognize their version #s - FF says they "Aren't compatible with Firefox 3.5.5", so I have to hit "Find updates" to make FF apply a "compatibility update". This happens every time I move FF from one computer to another...
Next, some of my addons' settings get screwed up. Brief, for example, refuses to recognize items marked as read after a FF transfer - if I mark an item as read on my laptop, then transfer FF to the desktop machine, Brief marks that item as unread. Ditto when transferring FF the other way...

Anybody got an idea why this is happening?

TIA!