How can I use the touchpad in Firefox?

I have sensory processing issues, including a severe strobe sensitivity, so I can't use Safari.

I have coordination issues, so I can't use touchpad tapping or gestures.

I usually use an external mouse. However, for the past few weeks I've been away from my desk and my externals, so I often end up using the touchpad. I am using Sierra, not High Sierra.

* Command-click no longer allows me to open a link in a new tab.

* Option-click doesn't either.

* Control-click is awkward but at least it opens a contextual menu.

* Function-click doesn't.

* Shift-click is awkward and opens a new window.