diff --git a/chrome/content/zotero/xpcom/mimeTypeHandler.js b/chrome/content/zotero/xpcom/mimeTypeHandler.js
index 84f444767..4d3b3f44b 100644
--- a/chrome/content/zotero/xpcom/mimeTypeHandler.js
+++ b/chrome/content/zotero/xpcom/mimeTypeHandler.js
@@ -55,30 +55,50 @@ Zotero.MIMETypeHandler = new function () {
 		_observers = [];
 		
 		if(Zotero.Prefs.get("parseEndNoteMIMETypes")) {
-			this.addHandler("application/x-endnote-refer", _importHandler, true);
-			this.addHandler("application/x-research-info-systems", _importHandler, true);
-			this.addHandler("application/x-inst-for-scientific-info", _importHandler, true);
-
-			this.addHandler("text/x-bibtex", _importHandler, true);
-			this.addHandler("application/x-bibtex", _importHandler, true);
-
-			//
-			// And some non-standard ones
-			//
-			this.addHandler("text/x-research-info-systems", _importHandler, true);
-			// Nature uses this one
-			this.addHandler("text/application/x-research-info-systems", _importHandler, true);
-			// Cell uses this one
-			this.addHandler("text/ris", _importHandler, true);
-			// Not even trying
-			this.addHandler("ris", _importHandler, true);
+			this.registerMetadataHandlers();
 		}
+		Zotero.Prefs.registerObserver("parseEndNoteMIMETypes", function(val) {
+			if (val) this.registerMetadataHandlers();
+			else this.unregisterMetadataHandlers();
+		}.bind(this));
+		
 		this.addHandler("application/vnd.citationstyles.style+xml", function(a1, a2) { Zotero.Styles.install(a1, a2) });
 		this.addHandler("text/x-csl", function(a1, a2) { Zotero.Styles.install(a1, a2) }); // deprecated
 		this.addHandler("application/x-zotero-schema", Zotero.Schema.importSchema);
 		this.addHandler("application/x-zotero-settings", Zotero.Prefs.importSettings);
 	}
 	
+	// MIME types that Zotero should handle when parseEndNoteMIMETypes preference
+	// is enabled
+	var metadataMIMETypes = [
+		"application/x-endnote-refer", "application/x-research-info-systems",
+		"application/x-inst-for-scientific-info",
+		"text/x-bibtex", "application/x-bibtex",
+		// Non-standard
+		"text/x-research-info-systems",
+		"text/application/x-research-info-systems", // Nature serves this
+		"text/ris", // Cell serves this
+		"ris" // Not even trying
+	];
+	
+	/**
+	 * Registers MIME types for parseEndNoteMIMETypes preference
+	 */
+	this.registerMetadataHandlers = function() {
+		for (var i=0; i<metadataMIMETypes.length; i++) {
+			this.addHandler(metadataMIMETypes[i], _importHandler, true);
+		}
+	}
+	
+	/**
+	 * Unregisters MIME types for parseEndNoteMIMETypes preference
+	 */
+	this.unregisterMetadataHandlers = function() {
+		for (var i=0; i<metadataMIMETypes.length; i++) {
+			this.removeHandler(metadataMIMETypes[i]);
+		}
+	}
+	
 	/**
 	 * Adds a handler to handle a specific MIME type
 	 * @param {String} type MIME type to handle
@@ -92,6 +112,18 @@ Zotero.MIMETypeHandler = new function () {
 		_ignoreContentDispositionTypes.push(type);
 	}
 	
+	/**
+	 * Removes a handler for a specific MIME type
+	 * @param {String} type MIME type to handle
+	 */
+	this.removeHandler = function(type) {
+		delete _typeHandlers[type];
+		var i = _ignoreContentDispositionTypes.indexOf(type);
+		if (i != -1) {
+			_ignoreContentDispositionTypes.splice(i, 1);
+		}
+	}
+	
 	/**
 	 * Adds an observer to inspect and possibly modify page headers
 	 */
@@ -107,7 +139,10 @@ Zotero.MIMETypeHandler = new function () {
 	 */
 	function _importHandler(string, uri, contentType, channel) {
 		var win = channel.notificationCallbacks.getInterface(Components.interfaces.nsIDOMWindow).top;
-		if(!win) throw "Attempt to import from a channel without an attached document refused";
+		if(!win) {
+			Zotero.debug("Attempt to import from a channel without an attached document refused");
+			return false;
+		}
 		
 		var hostPort = channel.URI.hostPort.replace(";", "_", "g");
 		
@@ -129,7 +164,7 @@ Zotero.MIMETypeHandler = new function () {
 			bag.setPropertyAsBool("allowTabModal", true);
 		
 			var continueDownload = prompt.confirmCheck(title, text, checkMsg, checkValue);
-			if(!continueDownload) return;
+			if(!continueDownload) return false;
 			if(checkValue.value) {
 				// add to allowed sites if desired
 				Zotero.Prefs.set("ingester.allowedSites", allowedSitesString+";"+hostPort);
@@ -148,12 +183,14 @@ Zotero.MIMETypeHandler = new function () {
 		var translators = translation.getTranslators();
 		if(!translators.length) {
 			// we lied. we can't really translate this file.
-			throw "No translator found for handled RIS, Refer or ISI file"
+			Zotero.debug("No translator found to handle this file");
+			return false;
 		}
 		
 		// translate using first available
 		translation.setTranslator(translators[0]);
 		frontWindow.Zotero_Browser.performTranslation(translation);
+		return true;
 	}
 	
 	/**
@@ -300,11 +337,16 @@ Zotero.MIMETypeHandler = new function () {
 		convStream.close();
 		inputStream.close();
 		
+		var handled = false;
 		try {
-			_typeHandlers[this._contentType](readString, (this._request.name ? this._request.name : null),
+			handled = _typeHandlers[this._contentType](readString, (this._request.name ? this._request.name : null),
 				this._contentType, channel);
 		} catch(e) {
-			// if there was an error, handle using nsIExternalHelperAppService
+			Zotero.debug(e);
+		}
+		
+		if (!handled) {
+			// handle using nsIExternalHelperAppService
 			var externalHelperAppService = Components.classes["@mozilla.org/uriloader/external-helper-app-service;1"].
 				getService(Components.interfaces.nsIExternalHelperAppService);
 			var frontWindow = Components.classes["@mozilla.org/embedcomp/window-watcher;1"].
@@ -317,10 +359,6 @@ Zotero.MIMETypeHandler = new function () {
 				streamListener.onDataAvailable(this._request, context, inputStream, 0, this._storageStream.length);
 				streamListener.onStopRequest(channel, context, status);
 			}
-			this._storageStream.close();
-			
-			// then throw our error
-			throw e;
 		}
 		
 		this._storageStream.close();
diff --git a/chrome/content/zotero/xpcom/zotero.js b/chrome/content/zotero/xpcom/zotero.js
index a4dde6524..3eea9f196 100644
--- a/chrome/content/zotero/xpcom/zotero.js
+++ b/chrome/content/zotero/xpcom/zotero.js
@@ -2291,6 +2291,133 @@ Zotero.Prefs = new function(){
 		// TODO: parse settings XML
 	}
 	
+	// Handlers for some Zotero preferences
+	var _handlers = [
+		[ "statusBarIcon", function(val) {
+			var doc = Components.classes["@mozilla.org/appshell/window-mediator;1"]
+						.getService(Components.interfaces.nsIWindowMediator)
+						.getMostRecentWindow("navigator:browser").document;
+			
+			var addonBar = doc.getElementById("addon-bar");
+			var icon = doc.getElementById("zotero-toolbar-button");
+			// When the customize window is open, toolbar buttons seem to
+			// become wrapped in toolbarpaletteitems, which we need to remove
+			// manually if we change the pref to hidden or else the customize
+			// window doesn't close.
+			var wrapper = doc.getElementById("wrapper-zotero-toolbar-button");
+			var palette = doc.getElementById("navigator-toolbox").palette;
+			var inAddonBar = false;
+			if (icon) {
+				// Because of the potential wrapper, don't just use .parentNode
+				var toolbar = Zotero.getAncestorByTagName(icon, "toolbar");
+				inAddonBar = toolbar == addonBar;
+			}
+			
+			if (val == 0) {
+				// If showing in add-on bar, hide
+				if (!icon || !inAddonBar) {
+					return;
+				}
+				palette.appendChild(icon);
+				if (wrapper) {
+					addonBar.removeChild(wrapper);
+				}
+				addonBar.setAttribute("currentset", addonBar.currentSet);
+				doc.persist(addonBar.id, "currentset");
+			}
+			else {
+				// If showing somewhere else, remove it from there
+				if (icon && !inAddonBar) {
+					palette.appendChild(icon);
+					if (wrapper) {
+						toolbar.removeChild(wrapper);
+					}
+					toolbar.setAttribute("currentset", toolbar.currentSet);
+					doc.persist(toolbar.id, "currentset");
+				}
+				
+				// If not showing in add-on bar, add
+				if (!inAddonBar) {
+					var icon = addonBar.insertItem("zotero-toolbar-button");
+					addonBar.setAttribute("currentset", addonBar.currentSet);
+					doc.persist(addonBar.id, "currentset");
+					addonBar.setAttribute("collapsed", false);
+					doc.persist(addonBar.id, "collapsed");
+				}
+				// And make small
+				if (val == 1) {
+					icon.setAttribute("compact", true);
+				}
+				// Or large
+				else if (val == 2) {
+					icon.removeAttribute("compact");
+				}
+			}
+		}],
+		[ "automaticScraperUpdates", function(val) {
+			if (val){
+				Zotero.Schema.updateFromRepository();
+			}
+			else {
+				Zotero.Schema.stopRepositoryTimer();
+			}
+		}],
+		[ "note.fontSize", function(val) {
+			if (val < 6) {
+				Zotero.Prefs.set('note.fontSize', 11);
+			}
+		}],
+		[ "zoteroDotOrgVersionHeader", function(val) {
+			if (val) {
+				Zotero.VersionHeader.register();
+			}
+			else {
+				Zotero.VersionHeader.unregister();
+			}
+		}],
+		[ "zoteroDotOrgVersionHeader", function(val) {
+			if (val) {
+				Zotero.VersionHeader.register();
+			}
+			else {
+				Zotero.VersionHeader.unregister();
+			}
+		}],
+		[ "sync.autoSync", function(val) {
+			if (val) {
+				Zotero.Sync.Runner.IdleListener.register();
+			}
+			else {
+				Zotero.Sync.Runner.IdleListener.unregister();
+			}
+		}],
+		[ "sync.fulltext.enabled", function(val) {
+			if (val) {
+				// Disable downgrades if full-text sync is enabled, since otherwise
+				// we could miss full-text content updates
+				if (Zotero.DB.valueQuery("SELECT version FROM version WHERE schema='userdata'") < 77) {
+					Zotero.DB.query("UPDATE version SET version=77 WHERE schema='userdata'");
+				}
+			}
+		}],
+		[ "search.quicksearch-mode", function(val) {
+			var wm = Components.classes["@mozilla.org/appshell/window-mediator;1"]
+						.getService(Components.interfaces.nsIWindowMediator);
+			var enumerator = wm.getEnumerator("navigator:browser");
+			while (enumerator.hasMoreElements()) {
+				var win = enumerator.getNext();
+				if (!win.ZoteroPane) continue;
+				Zotero.updateQuickSearchBox(win.ZoteroPane.document);
+			}
+			
+			var enumerator = wm.getEnumerator("zotero:item-selector");
+			while (enumerator.hasMoreElements()) {
+				var win = enumerator.getNext();
+				if (!win.Zotero) continue;
+				Zotero.updateQuickSearchBox(win.document);
+			}
+		}]
+	];
 	
 	//
 	// Methods to register a preferences observer
@@ -2298,6 +2425,11 @@ Zotero.Prefs = new function(){
 	function register(){
 		this.prefBranch.QueryInterface(Components.interfaces.nsIPrefBranch2);
 		this.prefBranch.addObserver("", this, false);
+		
+		// Register pre-set handlers
+		for (var i=0; i<_handlers.length; i++) {
+			this.registerObserver(_handlers[i][0], _handlers[i][1]);
+		}
 	}
 	
 	function unregister(){
@@ -2307,147 +2439,48 @@ Zotero.Prefs = new function(){
 		this.prefBranch.removeObserver("", this);
 	}
 	
+	/**
+	 * @param {nsIPrefBranch} subject The nsIPrefBranch we're observing (after appropriate QI)
+	 * @param {String} topic The string defined by NS_PREFBRANCH_PREFCHANGE_TOPIC_ID
+	 * @param {String} data The name of the pref that's been changed (relative to subject)
+	 */
 	function observe(subject, topic, data){
-		if(topic!="nsPref:changed"){
+		if (topic != "nsPref:changed" || !_observers[data] || !_observers[data].length) {
 			return;
 		}
 		
-		try {
-		
-		// subject is the nsIPrefBranch we're observing (after appropriate QI)
-		// data is the name of the pref that's been changed (relative to subject)
-		switch (data) {
-			case "statusBarIcon":
-				var doc = Components.classes["@mozilla.org/appshell/window-mediator;1"]
-							.getService(Components.interfaces.nsIWindowMediator)
-							.getMostRecentWindow("navigator:browser").document;
-				
-				var addonBar = doc.getElementById("addon-bar");
-				var icon = doc.getElementById("zotero-toolbar-button");
-				// When the customize window is open, toolbar buttons seem to
-				// become wrapped in toolbarpaletteitems, which we need to remove
-				// manually if we change the pref to hidden or else the customize
-				// window doesn't close.
-				var wrapper = doc.getElementById("wrapper-zotero-toolbar-button");
-				var palette = doc.getElementById("navigator-toolbox").palette;
-				var inAddonBar = false;
-				if (icon) {
-					// Because of the potential wrapper, don't just use .parentNode
-					var toolbar = Zotero.getAncestorByTagName(icon, "toolbar");
-					inAddonBar = toolbar == addonBar;
-				}
-				var val = this.get("statusBarIcon");
-				if (val == 0) {
-					// If showing in add-on bar, hide
-					if (!icon || !inAddonBar) {
-						return;
-					}
-					palette.appendChild(icon);
-					if (wrapper) {
-						addonBar.removeChild(wrapper);
-					}
-					addonBar.setAttribute("currentset", addonBar.currentSet);
-					doc.persist(addonBar.id, "currentset");
-				}
-				else {
-					// If showing somewhere else, remove it from there
-					if (icon && !inAddonBar) {
-						palette.appendChild(icon);
-						if (wrapper) {
-							toolbar.removeChild(wrapper);
-						}
-						toolbar.setAttribute("currentset", toolbar.currentSet);
-						doc.persist(toolbar.id, "currentset");
-					}
-					
-					// If not showing in add-on bar, add
-					if (!inAddonBar) {
-						var icon = addonBar.insertItem("zotero-toolbar-button");
-						addonBar.setAttribute("currentset", addonBar.currentSet);
-						doc.persist(addonBar.id, "currentset");
-						addonBar.setAttribute("collapsed", false);
-						doc.persist(addonBar.id, "collapsed");
-					}
-					// And make small
-					if (val == 1) {
-						icon.setAttribute("compact", true);
-					}
-					// Or large
-					else if (val == 2) {
-						icon.removeAttribute("compact");
-					}
-				}
-				break;
-			
-			case "automaticScraperUpdates":
-				if (this.get('automaticScraperUpdates')){
-					Zotero.Schema.updateFromRepository();
-				}
-				else {
-					Zotero.Schema.stopRepositoryTimer();
-				}
-				break;
-			
-			case "note.fontSize":
-				var val = this.get('note.fontSize');
-				if (val < 6) {
-					this.set('note.fontSize', 11);
-				}
-				break;
-			
-			case "zoteroDotOrgVersionHeader":
-				if (this.get("zoteroDotOrgVersionHeader")) {
-					Zotero.VersionHeader.register();
-				}
-				else {
-					Zotero.VersionHeader.unregister();
-				}
-				break;
-			
-			case "sync.autoSync":
-				if (this.get("sync.autoSync")) {
-					Zotero.Sync.Runner.IdleListener.register();
-				}
-				else {
-					Zotero.Sync.Runner.IdleListener.unregister();
-				}
-				break;
-			
-			// TEMP
-			case "sync.fulltext.enabled":
-				if (this.get("sync.fulltext.enabled")) {
-					// Disable downgrades if full-text sync is enabled, since otherwise
-					// we could miss full-text content updates
-					if (Zotero.DB.valueQuery("SELECT version FROM version WHERE schema='userdata'") < 77) {
-						Zotero.DB.query("UPDATE version SET version=77 WHERE schema='userdata'");
-					}
-				}
-				break;
-			
-			case "search.quicksearch-mode":
-				var wm = Components.classes["@mozilla.org/appshell/window-mediator;1"]
-							.getService(Components.interfaces.nsIWindowMediator);
-				var enumerator = wm.getEnumerator("navigator:browser");
-				while (enumerator.hasMoreElements()) {
-					var win = enumerator.getNext();
-					if (!win.ZoteroPane) continue;
-					Zotero.updateQuickSearchBox(win.ZoteroPane.document);
-				}
-				
-				var enumerator = wm.getEnumerator("zotero:item-selector");
-				while (enumerator.hasMoreElements()) {
-					var win = enumerator.getNext();
-					if (!win.Zotero) continue;
-					Zotero.updateQuickSearchBox(win.document);
-				}
-				break;
+		var obs = _observers[data];
+		for (var i=0; i<obs.length; i++) {
+			try {
+				obs[i](this.get(data));
+			}
+			catch (e) {
+				Zotero.debug("Error while executing preference observer handler for " + data);
+				Zotero.debug(e);
+			}
+		}
+	}
+	
+	var _observers = {};
+	this.registerObserver = function(name, handler) {
+		_observers[name] = _observers[name] || [];
+		_observers[name].push(handler);
+	}
+	
+	this.unregisterObserver = function(name, handler) {
+		var obs = _observers[name];
+		if (!obs) {
+			Zotero.debug("No preferences observer registered for " + name);
+			return;
 		}
 		
+		var i = obs.indexOf(handler);
+		if (i == -1) {
+			Zotero.debug("Handler was not registered for preference " + name);
+			return;
 		}
-		catch (e) {
-			Zotero.debug(e);
-			throw (e);
-		}
+		
+		obs.splice(i, 1);
 	}
 }