<p>I'd like to have my Eclipse plugin cause a URL to be opened by the users' default browser. This seems like pretty standard behavior, but I haven't been able to find any docs on how to do this.</p>

<p>Can anyone help?</p>

Do you mean launch an external windows (IE, FireFox, ...) outside eclipse, or opening an internal "
Browser
" composite ?
Because on the internal side, the
org.eclipse.help.ui.internal.browser.embedded.EmbeddedBrowser
seems to be able to define any kind of major browser.
To open the default user's browser (as an internal or external window) is a preference defined in General/Web browser.