Ensure you have a version of Firefox before version 57. TiddlyFox will not work with Firefox 57 and on. For Firefox 57 and on, consider using the following instead:
Install the latest release of the TiddlyFox extension from:
If you are using TiddlyFox v1.x.x, you will need to click OK in response to the prompt from TiddlyFox that asks whether to enable saving for this file
If you are using TiddlyFox v2.x.x you will need to click on the icon of a kitten standing on a blue globe to activate saving. There is no prompt in v2.0.1.
For TiddlyFox v2.0.1, you can not be using Private Browsing mode nor can you be using "Never Remember History".
Try creating a new tiddler using the new tiddler button in the sidebar. Type some content for the tiddler, and click the ok button
Save your changes by clicking the save changes button in the sidebar
Look for the yellow notification Saved wiki at the top right of the window
Refresh the browser window to verify that your changes have been saved correctly