Firefox compatibility fixes:

Replaced all chrome.tabs. async calls with browser.tabs. (Firefox's chrome compatibility shim does not return Promises for tabs APIs)
Replaced chrome.webRequest.onBeforeSendHeaders with browser.webRequest equivalent
Replaced chrome.runtime.sendMessage() in the popup with browser.runtime.sendMessage() to correctly receive responses from the background
Added "persistent": true to the background declaration to prevent the background page from being unloaded between events, which caused the captured token to be lost before the popup could retrieve it

Added Firefox-compatible background fallback configuration to support review and runtime compatibility.
Kept the one-click Bandai token handoff flow unchanged.
Improved user-facing error guidance when extension messaging is unavailable.