add_task(async function test() { await SpecialPowers.pushPrefEnv({ set: [["browser.tabs.remote.separateFileUriProcess", true]], }); let fileData = ""; for (var i = 0; i < 100; ++i) { fileData += "hello world!"; } let file = Cc["@mozilla.org/file/directory_service;1"] .getService(Ci.nsIDirectoryService) .QueryInterface(Ci.nsIProperties) .get("ProfD", Ci.nsIFile); file.append("file.txt"); file.createUnique(Ci.nsIFile.NORMAL_FILE_TYPE, 0o600); let outStream = Cc[ "@mozilla.org/network/file-output-stream;1" ].createInstance(Ci.nsIFileOutputStream); outStream.init( file, 0x02 | 0x08 | 0x20, // write, create, truncate 0o666, 0 ); outStream.write(fileData, fileData.length); outStream.close(); let fileHandler = Cc["@mozilla.org/network/io-service;1"] .getService(Ci.nsIIOService) .getProtocolHandler("file") .QueryInterface(Ci.nsIFileProtocolHandler); let fileURL = fileHandler.getURLSpecFromActualFile(file); info("Opening url: " + fileURL); let tab = BrowserTestUtils.addTab(gBrowser, fileURL); let browser = gBrowser.getBrowserForTab(tab); await BrowserTestUtils.browserLoaded(browser); let blob = await SpecialPowers.spawn( browser, [file.leafName], function (fileName) { return new content.window.Promise(resolve => { content.window .fetch(fileName) .then(r => r.blob()) .then(blob => resolve(blob)); }); } ); ok(File.isInstance(blob), "We have a file"); is(blob.size, file.fileSize, "The size matches"); is(blob.name, file.leafName, "The name is correct"); file.remove(false); gBrowser.removeTab(tab); });