how to make Webextension content_scripts load on opened pages after the first?

Problem: The content_scripts specified in the manifest.json of a WebExtension are only applied to the first page loaded in a window created by the extension regardless of how non-specific my matches are.

Details: I’m making an extension for a bookmarking site.
The plugin opens a window with a form at /bookmarks/new. Content scripts are injected at this point. The user then fills in and submits the form.

IF the form successfully submits it redirects to /bookmarks/success content scripts are NOT injected here even if one of my matches is "*://*/*"

Questions:

1. Is it possible for content_scripts to be injected into subsequent page loads using only instructions in the manifest.json?
2. If not, is there something I can add a listener to in the extension that will tell me about page changes & their url?

I’m currently testing in Firefox, but I’m hoping to make this extension work in it and Chrome.

I’ve failed to find answers to either of these questions.