Components.interfaces.nsIMsgCompDeliverModensIMsgCompSendFormatnsIMsgCompConvertiblensIMsgCompTypensIMsgCompFormatnsIAbPreferMailFormatnsIPlaintextEditorMailnsISupportsStringmozISpellCheckingEnginedocument.getElementById(), document.querySelectorAll() or similar methods. The documents these methods have been used with have probably changed dramatically. Check out searchfox.org to learn about the current layouts.<listbox> related elements have been removed. Use<richlistbox> instead. A <richlistbox> does not support cells or columns, just one <richlistitem> per row (which can contain multiple other elements like hbox, vbox, labelor image elements)listbox/richtlistboxmethods have been removed and can be replaced as follows:listbox.appendItem(label, value):listbox.insertItemAt(index, label, value):listbox.removeItemAt(index):dialog as follows:DOCTYPE changed and the preference attribute now contains the full ID of the preference. If you used more than one prefpane you need to rework the UI into tabs.preferencesBindings.js at the bottom, which is mandatory to recreate the functionality of the preference attribute. It is also mandatory, that you include a custom JavaScript file (aspreferences.js in the above example) afterwards, which defines the types of the used preferences (which was formerly done inside the preferences tag). The file can be as short as this:type attribute and a cancel button to the dialog:preference attribute (and preferencesBindings.js) and directly use the preferences service instead. Check out options.xul and options.js of the Shrunked Image Resizer.hboxelements with an appropriate class identifier:hbox as a replacement for the statusbarpanel, like label or image.menulist no longer supports the editable attribute. However, editable menulists have been re-implemented as custom elements. To be able to use it, you need some extra files to be linked from your document:menupopup element is defined as a direct child of the menulist element in the above example, it cannot be accessed bymenupop element, or get it bymenulist element.groupbox tag continues to work, the caption tag has been removed. Use the following now:datetimepicker, which can be used.Date object:datetimepicker, the following CSS files need to be included:let notifyBox = specialTabs.msgNotificationBar;let notifyBox = gNotification.notificationbox;let notifyBox = gMessageNotificationBar.msgNotificationBar;let notifyBox = gNotification.notificationbox;notifyBox.removeAllNotifications();let notification = notifyBox.getNotificationWithValue(value);notificationbox.removeNotification(notification);mail-multi-emailHeaderField has been renamed into mail-multi-emailheaderfield (no camelCase anymore).treecol can be either shown or hidden via the column picker. Up to TB68 the column picker closed after a column had been selected/toggled. By adding closemenu="none" to a treecol, the column picker stays open after the display state of associated treecol has been toggled.<dialog> and you wanted to respond to the buttons being pressed, you’d have something like this:preventDefault(). A return value is not needed.ondialogaccept, ondialogextra1, ondialogextra2 and ondialogcancel.<dialog> events also applies to all onwizard… events on <wizard>, and onpage… events on <wizardpage>..jsm extension. Most notably:mailServices.js has been renamed to MailServices.jsm. This change was originally backwards-compatible with a deprecation warning, but the changes to module importing (see below) made that pointless and the old file has now been removed completely.MailUtils.js is now MailUtils.jsm.MailUtils.getFolderForUri was renamed to MailUtils.getExistingFolder.ChromeUtils.import is a replacement for Components.utils.import (which was also changed in this way). Note that no second argument is supplied. The returned object is a dictionary of only the objects listed in EXPORTED_SYMBOLS.defaultAccount member can (since TB 65) have a null value - if for some reason it doesn't have, or can't work out, the default account.onDataAvailable method lost its context argument. This was removed in bug 1525319 which breaks the API.onStartRequest and onStopRequest methods also no longer have a context argument, which could be detected in a similar way.newChannel was removed and newChannel2 was renamed to newChannel. (Bug 1528971.)newChannel has been unused for a long time it should be safe to just replace the old newChannel implementation with the newChannel2 and forward calls from newChannel2.convertFromByteArray has been removed. The new preferred way to deal with unicode is through the TextEncoder and TextDecoder classes.Element, Node, etc. instead, which are now available in all scopes.Cc[...].createInstance(Ci....), but simply via the new keyword:new DOMParser();new XMLSerializer();new XMLHttpRequest();Cu.importGlobalProperties(["DOMParser"]);Cu.importGlobalProperties(["XMLSerializer"]);Cu.importGlobalProperties(["XMLHttpRequest"]);tree object is now a XULTreeElement. It has lost thetreeBoxObject property, because the nsITreeBoxObject has been removed. Most of its methods can now be accessed directly through the tree object. For example:nsITreeColumn has been replaced by the TreeColumn object. Even though their interfaces look the same, they could behave differently. Check your implementation, as this affects almost all methods of nsITreeView.TreeColumn parameter, a simple { id: columnName } object no longer works. Get a proper TreeColumn object via tree.columns.getNamedColumn(columnName).TreeColumn object no longer has a selectable attribute and nsITreeView has lost its isSelectable() method.