Yes (and no…) “Try free edition” implies non-free (as in speech) to me, but here that seems not the case. [Maybe you meant “no-cost” anyway? That also applies.]
I confirmed PlotlyJS (and Plotly that uses it) are under the MIT “Expat” License.
It seems you should have no freedom issues as in PlotlyJS.jl github repo, I also see same MIT for dependency:
https://raw.githubusercontent.com/sglyon/PlotlyJS.jl/master/deps/plotly-latest.min.js
[Good luck with reading that minified code… 
it’s still “free software”; just wouldn’t be “GPL-compatible”… In general that would mean not ok to distribute with GPL… (LGPL would be ok) but “arms-length” probably applies here, and js runs in the browser (another process) so I’m pretty sure you’re ok (at least if your GPL would be in non-browser).]
I didn’t check further (other dependencies), it seems everything running on your machine is free. I’m not sure SaaS applies, if so you might have other concerns with that (see Stallman on that too…)…
Not sure what you’re paying for (optionally) - didn’t check - probably just some optional convenience features.