One of the annoyances with web-based email such as GMail is that you don't normally get a new mail/message waiting alert the way you do if you use browser-based email such as SeaMonkey or desktop-based email such as Thunderbird. To overcome this, Google offers a Desktop GMail Notifier applet. However, it is not cross-platform and is currently available only for Windows and Mac. Several third parties offer Firefox browser extensions as another solution. These include GMail Notifier, GMail Manager GMail Checker, and WebMail Notifier. Each of these suffers the problem that by default they access the web-based inbox using GMail's version 2 interface, which is intolerably slow on dialup connections.
WebMail Notifier has the advantage that it supports user login scripts, allowing one to change this and other behaviors. It comes with a GMail script, webmail4.js, which shows on the menu as GMail. I made a slightly modified version of this script, Webmail Notifier G/HTML (2008g13-webmail-notifier-gmail-html.js). This adds G/Html to the menu. G/Html bypasses GMail's standard (version 2) 'loading' screen and goes directly to the basic HTML interface. For dialup connections and slow computers this is far faster than the standard interface. Unlike webmail4.js, this script won't automatically adapt between gmail.com and googlemail.com; you'll have to set it manually. Also, this script will not bring up the basic html view for Google Apps. No URL syntax for accomplishing that has been published. Finally, this script is hard coded to show is:unread in:inbox, which I find much more useful than showing is:unread generally. You'll need to edit the script if you want different settings. Using a script for such things has an advantage over just modifying webmail4.js directly: a script won't be overwritten during WebMail Notifier's rather frequent updates. Note: The script this page links to was updated July 30, 2008 and should be working correctly again.
You still have to set the preferences of WebMail Notifier manually, including username and login, and whether to login automatically. You have the option to have it notify you only for new mail. Most notifiers remind you every time they poll if you have any unread messages, even if they are not new since the last poll. That's rather like message waiting on a hotel phone and can be intrusive. With the new mail only setting, WebMail Notifier won't bug you about messages you choose to leave unread. You can also set a sound to tell you about new mail. I used Hal from 2001, announcing that there is a message for you. You'll have to get your own sound; clips of Hal's voice or anything else from the movies are undoubtedly copyrighted so I can't provide them here. Finally, you have to set the polling interval. This probably shouldn't be less than 10 minutes, since that's about the minimum useful uninterrupted work interval. A longer period may be desirable with dial-on-demand, because whenever the browser is running, whether for browsing local files or just because it wasn't closed, the PC may dial the net at this interval to check for new mail. There is at least one email provider who charges extra for polling intervals less than 2 hours, but that's probably too long for comfort.