Right now, on average, each component registration uses about 300 bytes. We have almost 700 of them. That adds up to significant overhead. Lots of them can be easily gotten rid of. Many are only ever used from C++. Those can be replaced with singleton getters and constructors. Some are, for reasons that defy explanation, implemented in and used only by JS. Those can be replaced with, well, JS. A lot of them are just entirely unused. All of the following registrations can be gotten rid of with minimal effort: @mozilla.org/accessibleRetrieval;1 @mozilla.org/addons/policy-service;1 @mozilla.org/addons/remote-tag-service;1 @mozilla.org/audiochannel/service;1 @mozilla.org/audiochannelagent;1 @mozilla.org/autoconfiguration;1 @mozilla.org/browser/feeds/result-service;1 @mozilla.org/browser/livemark-service;2 @mozilla.org/browser/session-history-transaction;1 @mozilla.org/categorymanager;1 @mozilla.org/content/post-content-iterator;1 @mozilla.org/content/pre-content-iterator;1 @mozilla.org/content/subtree-content-iterator;1 @mozilla.org/cookieService;1 @mozilla.org/cspservice;1 @mozilla.org/cycle-collector-logger;1 @mozilla.org/dirIndex;1 @mozilla.org/dirIndexParser;1 @mozilla.org/dom/sessionStorage-manager;1 @mozilla.org/dom/storagemanager;1 @mozilla.org/dom/window-controller;1 @mozilla.org/editor/editingcontroller;1 @mozilla.org/editor/editingsession;1 @mozilla.org/editor/editorcontroller;1 @mozilla.org/editor/editordocstatecontroller;1 @mozilla.org/editor/htmleditor;1 @mozilla.org/editor/htmleditorcontroller;1 @mozilla.org/editor/texteditor;1 @mozilla.org/editor/txtsrvfiltermail;1 @mozilla.org/embedcomp/appstartup-notifier;1 @mozilla.org/embedcomp/base-command-controller;1 @mozilla.org/embedcomp/command-manager;1 @mozilla.org/embedcomp/controller-command-group;1 @mozilla.org/embedcomp/controller-command-table;1 @mozilla.org/embedcomp/find;1 @mozilla.org/embedding/browser/nsWebBrowser;1 @mozilla.org/embeddor.implemented/bookmark-charset-resolver;1 @mozilla.org/feed-entry;1 @mozilla.org/feed-generator;1 @mozilla.org/feed-person;1 @mozilla.org/feed-processor;1 @mozilla.org/feed-result;1 @mozilla.org/feed-textconstruct;1 @mozilla.org/feed;1 @mozilla.org/geolocation/service;1 @mozilla.org/gfx/devicecontextspec;1 @mozilla.org/gfx/printsession;1 @mozilla.org/image/loader;1 @mozilla.org/image/request;1 @mozilla.org/intl/collation;1 @mozilla.org/intl/utf8converterservice;1 @mozilla.org/js/xpc/ContextStack;1 @mozilla.org/js/xpc/ID;1 @mozilla.org/js/xpc/XPConnect;1 @mozilla.org/login-manager/crypto/SDR;1 @mozilla.org/login-manager/loginInfo;1 @mozilla.org/login-manager/prompter;1 @mozilla.org/login-manager/storage/json;1 @mozilla.org/network/application-cache-namespace;1 @mozilla.org/network/application-cache;1 @mozilla.org/network/background-channel-registrar;1 @mozilla.org/network/content-sniffer;1 @mozilla.org/network/file-stream;1 @mozilla.org/network/http-channel-auth-provider;1 @mozilla.org/network/request-context-service;1 @mozilla.org/network/request-observer-proxy;1 @mozilla.org/network/socket-provider-service;1 @mozilla.org/network/sync-stream-listener;1 @mozilla.org/server/jshttp;1 @mozilla.org/offlinecacheupdate;1 @mozilla.org/passwordmanager/authpromptfactory;1 @mozilla.org/peerconnection;1 @mozilla.org/power/powermanagerservice;1 @mozilla.org/pref-relativefile;1 @mozilla.org/presentation/datachanneltransport;1 @mozilla.org/properties;1 @mozilla.org/redirectchannelregistrar;1 @mozilla.org/remote-web-navigation;1 @mozilla.org/remote/marionette;1 @mozilla.org/nsGeneratingKeypairInfoDialogs;1 @mozilla.org/nsTokenDialogs;1 @mozilla.org/security/keyobject;1 @mozilla.org/security/psmdownload;1 @mozilla.org/securityconsole/message;1 @mozilla.org/spellchecker;1 @mozilla.org/synth-voice-registry;1 @mozilla.org/toolkit/disk-space-watcher;1 @mozilla.org/toolkit/native-app-support;1 @mozilla.org/toolkit/remote-service;1 @mozilla.org/transactionmanager;1 @mozilla.org/udp-socket-child;1 @mozilla.org/uriclassifierservice @mozilla.org/url-classifier/jslib;1 @mozilla.org/userinfo;1 @mozilla.org/chrome/chrome-native-theme;1 @mozilla.org/widget/appshell/gtk;1 @mozilla.org/widget/bidikeyboard;1 @mozilla.org/widget/image-to-gdk-pixbuf;1 @mozilla.org/widget/printdialog-service;1 @mozilla.org/widget/window/gtk;1 @mozilla.org/widgets/child_window/gtk;1 @mozilla.org/thread-pool;1 @mozilla.org/xpcom/error-service;1 @mozilla.org/xre/runtime;1 @mozilla.org/layout/form-processor;1 @mozilla.org/layout/xul-boxobject-menu;1 @mozilla.org/layout/xul-boxobject-tree;1 @mozilla.org/layout/xul-boxobject;1 @mozilla.org/svg/svg-document;1 @mozilla.org/xml/xml-document;1 @mozilla.org/xul/xul-controllers;1 @mozilla.org/xul/xul-sort-service;1 And I have ideas about how to get rid of: @mozilla.org/supports-PRBool;1 @mozilla.org/supports-PRInt16;1 @mozilla.org/supports-PRInt32;1 @mozilla.org/supports-PRInt64;1 @mozilla.org/supports-PRTime;1 @mozilla.org/supports-PRUint16;1 @mozilla.org/supports-PRUint32;1 @mozilla.org/supports-PRUint64;1 @mozilla.org/supports-PRUint8;1 @mozilla.org/supports-char;1 @mozilla.org/supports-cstring;1 @mozilla.org/supports-double;1 @mozilla.org/supports-float;1 @mozilla.org/supports-id;1 @mozilla.org/supports-interface-pointer;1 @mozilla.org/supports-string;1

Kris, any chance you could regenerate the list in comment 0? That list is now quite stale and it's a lot of work to fish for new things from it. (BTW I've also found quite a few XPCOM classes that should have been on that list but weren't while looking around, FWIW.) Thanks!

Unfortunately, it was a pretty manual process, with some code to spit out every contract ID that was registered on Linux, and then me individually checking how they were used. Here's the original list filtered to only include contracts that are still in Cc in my latest m-c build, though: @mozilla.org/accessibleRetrieval;1 @mozilla.org/addons/policy-service;1 @mozilla.org/browser/livemark-service;2 @mozilla.org/categorymanager;1 @mozilla.org/cookieService;1 @mozilla.org/cspservice;1 @mozilla.org/embedding/browser/nsWebBrowser;1 @mozilla.org/feed-entry;1 @mozilla.org/feed-generator;1 @mozilla.org/feed-person;1 @mozilla.org/feed-processor;1 @mozilla.org/feed-result;1 @mozilla.org/feed-textconstruct;1 @mozilla.org/feed;1 @mozilla.org/gfx/devicecontextspec;1 @mozilla.org/gfx/printsession;1 @mozilla.org/image/loader;1 @mozilla.org/image/request;1 @mozilla.org/login-manager/crypto/SDR;1 @mozilla.org/login-manager/loginInfo;1 @mozilla.org/login-manager/prompter;1 @mozilla.org/login-manager/storage/json;1 @mozilla.org/passwordmanager/authpromptfactory;1 @mozilla.org/peerconnection;1 @mozilla.org/power/powermanagerservice;1 @mozilla.org/presentation/datachanneltransport;1 @mozilla.org/remote-web-navigation;1 @mozilla.org/remote/marionette;1 @mozilla.org/nsGeneratingKeypairInfoDialogs;1 @mozilla.org/nsTokenDialogs;1 @mozilla.org/security/keyobject;1 @mozilla.org/security/psmdownload;1 @mozilla.org/securityconsole/message;1 @mozilla.org/synth-voice-registry;1 @mozilla.org/toolkit/remote-service;1 @mozilla.org/udp-socket-child;1 @mozilla.org/uriclassifierservice @mozilla.org/url-classifier/jslib;1 @mozilla.org/userinfo;1 @mozilla.org/widget/appshell/gtk;1 @mozilla.org/widget/image-to-gdk-pixbuf;1 @mozilla.org/widget/printdialog-service;1 @mozilla.org/xpcom/error-service;1 @mozilla.org/xre/runtime;1 @mozilla.org/layout/form-processor;1