hack to avoid injecting SingleFile scripts too early

cli/back-ends/webdriver-gecko.js

@@ -82,6 +82,9 @@ exports.getPageData = async options => {
 			await driver.sleep(3000);
 		}
 		await driver.get(options.url);
+		while (await driver.getCurrentUrl() == "about:blank") {
+			// do nothing
+		}
 		scripts = scripts.replace(/\n(this)\.([^ ]+) = (this)\.([^ ]+) \|\|/g, "\nwindow.$2 = window.$4 ||");
 		await driver.executeScript(scripts);
 		if (options.browserWaitUntil != "domcontentloaded") {