updated
So did some further debugging, and actually my content script is being called twice, for some reason?
Again this all started with FF52, where it seems some serious backend addon adjustments were made, with little/no patch notes about the content.
Offending code:
Background.js
browser.tabs.onUpdated.addListener( function (tabId, changeInfo, tab) {
if (changeInfo.status == "complete" && tab.active) {
browser.tabs.executeScript(null, {file: "content_script.js"});
}
});
content_script.js
console.log(“You should see me once.”);