Hi,

I spent some time around these issues and found out the following

1. The popup doesn't appear to work - Apparently, firefox for android does not support much of the APIs needed by this extension. (https://developer.mozilla.org/en-US/Add-ons/WebExtensions/manifest.json/browser_action#Browser_compatibility). I have created a bug in bugzilla to support this. (Link - https://bugzilla.mozilla.org/show_bug.cgi?id=1393911)

2. Let's me add URLs but doesn't change behaviour -
Only the "hostname" part of the URL is expected to be entered in the settings.
I was able to see links opened in a new tab in android for hackernews, reddit, twitter etc.,
You can use https://www.freeformatter.com/url-parser-query-string-splitter.html to get the hostname for a given URL.

3. When I add a few URLs, the space to add a new URL also disappears - This is a bug being worked on by mozilla and was fixed in firefox 57. Link - https://bugzilla.mozilla.org/show_bug.cgi?id=1386316

Since there is nothing much I can do here, I will add warnings for android users about the features missing in android in the addon's description.

Thanks