[Firefox Nightly Android] Content script loads only after opening the add-on 'popup'

I created an add-on that manipulates a site’s HTML based on the settings the user chooses in the add-on’s settings (the settings are saved with ‘chrome.storage.local’, I just ported my code from chrome and it worked).
When the user opens a specific website, the add-on is supposed to run a continuous (interval) script that changes the HTML, the problem is that it doesn’t, it requires the user to load the site, then open the add-on settings, then return to the site, and then it starts working.
How can I fix that? How do I make the script run when the user opens the site? This is a problem only on android, not chrome or desktop firefox