Please note that you need to explicitly enable TiddlyFox 2.x for each TiddlyWiki file that you want to use with it.
When you first load a TiddlyWiki file from a file:// URI the TiddlyFox toolbar icon will show a blue ball. Clicking it will bring up a panel with a big green "Enable" button that enables saving for that file. The TiddlyFox toolbar icon then switches to green to indicate that saving is enabled.
The permission settings are preserved between sessions, but are not carried over from earlier versions of TiddlyFox.
Note that the latest versions of TiddlyFox are not compatible with older versions of Firefox. If you can't upgrade to a later copy of Firefox, you can use the older version 1.0alpha18.1-signed.1-signed version from: