When starting in Connector mode (i.e. Standalone is open), Zotero first starts in Full mode, looks for Standalone, then "shuts down" and restarts in Connector mode. `Zotero.shutdown()` returns a promise which is then followed up by a `Zotero.init` call. Thus, when starting in Connector mode, Zotero initialization is asynchronous and makes it possible for `Zotero_Browser.init()` to be called before `Zotero.initialized` is true, which prevents `Zotero_Browser` from initializing. Additionally, even if `Zotero_Browser.init()` is called after Zotero is initialized in Connector mode, it is possible that `Zotero_Browser.init()` will be called _after_ the "load" event for browser.xul has already fired, so `chromeLoad` is never called. This patch ensures that both of these race conditions are taken into account.
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