Yeah it’s a funky thing, blank in the URL bar means about:blank or about:newtab. To verify, after that blank tab opens, open borwser console, then type this code:
Sorry I dont know what is gBrowser. I am reading some information about it to understand it more.
E.g. “gBrowser is only accessible from the scope of the browser window (browser.xul)” But I do not know what is the xul.
“You can access gBrowser only after the browser window is fully loaded. If you need to do something with gBrowser right after the window is opened, listen for the load event and use gBrowser in the event listener.”
When the header and scripts are not loaded, how can you add a listener?
Yes, you are correct in your assumption that you cannot attach to about:blank. Instead you should load your own page in a tab (which could already have the content you need).