Mozilla Firefox is set to delete and clear everything each time I close the program, which I’ve done. I brought up the website on IE on the same computer and the button is there, so the issue is specific to Mozilla Firefox.
Click on Help in FF and do a restart with Add-ons disabled. It may be an Add-on that you installed.
You can also click on help and then click on Troubleshooting Information. In the upper right corner you will see a button to Refresh FireFox. This fixes a lot of weird things that happen in FF.