How to turn off Firefox forms autocomplete for only certain websites, or for all sites temporarily?
The Form History Control extension for Firefox allows you to clear the AutoComplete storage for specific websites, and supports many other advanced AutoComplete tasks.
Go to my JSFiddle example.
In the bottom right corner there is a link with the text ACOff.
Drag this link to your bookmark toolbar.
Now go to your website - click the link, and all fields with type=text have their autocomplete turned off.