Collection of Google Calendar Firefox extensions
There is a good collection of Firefox extensions for Google calendar users, I find it with great help especially that I'm very lazy to use a calendar to organize any event.
As its name indicates the extension provides robust notifications and display of your Google Calendars for today, as well as showing any upcoming all day events for tomorrow. Colors could be customized for each label/feed, in addition to timezone options, and other notification options.

A quick shortcut to add calendar entries without having to open a Google Calendar page.
GCalQuickTab makes it easy to switch between Gmail and Google Calendar by overriding the default behavior of the new web apps links that appear in the upper-left-hand corner of those sites. If the linked webapp is already open, then it brings that tab into focus instead of opening the webapp in a new window. You can also switch apps by using keyboard shortcuts: 'g' for Gmail and 'l' for Calendar.

Simple statusbar-Addon that links to google calendar. The extension is really basic right now: left click opens it in current tab, middle click in new tab, and right click in new window.
If you know more extensions for Google Calendar, add it in comments or suggest feature that you'd love to have in a Firefox extension for GCal.

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