Change accesskey modifier keys in Firefox

Question

I'm working on a website where each page has buttons, like "submit" and "cancel". Each of these buttons has an accesskey attribute. The submit button's accesskey attribute is set to S, and the cancel button's accesskey attribute is set to C.

Access keys are activated using different modifiers in different browsers. Internet Explorer, Safari, and Google Chrome use just the alt, while Firefox uses both the alt and the shift keys. As well, Firefox uses alt + s to open the history menu.

Answers to this question should not suggest changing settings in the browser's configuration as that would not be feasible on a production site.

How I change the modifier keys that Firefox uses for accesskey's to just alt, and prevent the history menu from opening?

I am working in Ubuntu 16.04.