Cookies are probably enabled already, but try the steps in this article to access the Options page:

Websites say cookies are blocked - Unblock them

Are you accessing the problem site in a private window?

In adddition to the above :

The header of your question reads : " how to access tools "

Answer : Press the Alt key on your keyboard and look at the upper left of your screen.

You can also open the Options/Preferences page via the "3-bar" Firefox menu button.

Note that cookies are normally enabled by default.

If you use extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) that can block (wanted) content (Adblock Plus, NoScript, Disconnect, Ghostery, Privacy Badger, uBlock Origin) always make sure such extensions do not block (wanted) content.

• make sure your extensions and filters are updated to the latest version
• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

Firefox shows the shield icon at the left end of the location/address bar in case content is blocked by Tracking Protection.

• click the shield icon for more detail and possibly disable the protection
• You can check the Web Console by Tracking Protection
• "3-bar" menu button or Tools -> Web Developer
• https://support.mozilla.org/en-US/kb/tracking-protection-firefox

cor-el said

You can also open the Options/Preferences page via the "3-bar" Firefox menu button.

As mentioned in the article that jscher2000 provided a link to.