Firefox v10 Portable About:Config CACHE Pathing issues

I've enabled CACHE for Firefox 10 portable, I have changed:
"browser.cache.disk.parent_directory = C:\Windows\Temp"
It works all find and dandy, pages load much faster then over riding cache to 0.

However this is the issue. It keeps resetting the pathing from C to U (my thumb drive). I will not keep MY pathing I enter. Here is my setup. I run Ff10p from my C drive while at home. I sync it to my U thumb drive when I go to work. I run it from my U (thumb drive) while at work, and that is where it changed my entered path to U instead of keeping it C.

So I notice it creates a U:\Windows\Temp folder on my U (thumb drive).
I have to enter about:config again and change the U to a C, close Ff10p and reopen it and it works from there, just like at home.

When I get home and sync it back to my C drive, it still keeps my C:\Windows\Temp pathing with no issues. But when I get to work again it changes the setting again.

So what gives? Why is it over writing settings on its own?
How can I "hard code" it to keep my pathing?

Update:
No responses for a week now, but responses to some chrome post, alright.
I disabled browser.cache.disk.parent_directory
Used disk.cache.memory.capacity = 131072 instead.
About as "snappy and responsive as disk cache, but FF uses about 800mbs ram instead of around 400 with cache on disk.