Like Google Talk, you can consider placing your favorite Google services like Gmail, Google Reader, Google Calendar, etc. in the Firefox sidebar so that content is always accessible without you having to switch any tabs in Firefox.

gmail firefox sidebar 
Figure 1: Gmail Inbox placed inside Firefox Sidebar

Here are some popular Google websites & tools that can added to the Firefox Sidebar. Thanks Steve for the idea.

Google Gmail – http://m.gmail.com – With Gmail running in the sidebar, you can compose new emails, browse your Google contacts or get notified of new emails in Gmail.

Google Notebook – http://www.google.com/notebook/m – The mobile version of Google Notebook lets you browse existing notes or add new notes from the Firefox Sidebar.

If you want to do more, add the desktop version of Google Notebook to Firefox Sidebar using this address – http://www.google.com/notebook/ig?hl=__MSG_locale__

google-notebook-firefox 

Related: Save Google Results in Google Notebook

Google Talk – http://talkgadget.google.com/talkgadget/popout – You have this already in your Firefox sidebar but just in case.

Google Homepage – http://www.google.com/ig/i – This is the iPhone optimized version of Google IG but the layout looks just perfect in the Firefox Sidebar and requires no extensions.

Google News – http://www.google.com/m/news – This is the regular Google News homepage with stories from all categories. If you like to see only technology related news in the Firefox Sidebar, use http://www.google.com/m/news?topic=t

google-docs-sidebarGoogle Docs – http://docs.google.com/m – With the mobile version of Google Docs, you can browse existing documents but can’t create new stuff.

You may however use Google Docs shortcuts to quickly create new documents, spreadsheets or presentations from Firefox Sidebar.

If you are just looking to browse documents, also try the following URL as it gives you an option to instantly search Google Docs documents.
http://docs.google.com/API/IGoogle?up_numDocuments=100&browserok=true

google-calendar-mobile

Google Calendar – http://www.google.com/calendar/m – Keep track of upcoming events and appointments by placing Google Calendar in the Firefox sidebar. You also get the option to add new events to your Google Calendar.

Google Reader – http://www.google.com/reader/i – This is also for the iPhone but you can use it it catch up with you favorite RSS feeds while surfing the web in Firefox.

Google Photos – http://picasaweb.google.com/m/ – This lets you browse Picasa Web Album photos in the Firefox sidebar. You may also put comments on Photos.

Orkut – http://m.orkut.com – You can read new scraps, manage friend requests or track updates from your existing Orkut friends using the mobile version of Orkut.

Related: How to access websites using email