Hi team,
I’m currently looking into adding our safari mobile extension to Firefox Android. We are currently using sendNativeMessage in some part of our code, but I do see that it is listed as not available for Firefox Android here. However, I do see it’s listed as supported in MDN. I figured it would be best to just ask the community to get the most accurate answer. Which one should I trust and why are they conflicting?
I honestly don’t know anything for sure. I have never tried making extensions for Android-version of Firefox.
But I notice that bottom of page you link on extensionworkshop.com says
Last update: mdnwebdocs-bot Sep 15, 2020
A lot has happened with Firefox for Android since then, so I would trust MDN here. At least until the point you try it in practice 
Thanks for calling out this issue. When I looked into it last week, I found that connectNative() and sendNativeMessage() are only available in GeckoView, which is used by Firefox for Android.
Last week we landed PR 21115 to correct the data for sendNativeMessage() but we missed the other method. I just opened PR 21133 to add a little more information to the compatibility notes.