Version 2.0 of LibX is available for Firefox and Chrome, but the Firefox version is running into difficulty with the new way Firefox is verifying extensions. If you're only interested in the proxy support, you might want to use the bookmarklet instead.
LibX Caltech edition is an extension which will let you access the library’s resources directly from your browser. It adds a Caltech Library icon to the upper right corner of your browser with an interface to search the library catalog and will also add a right-mouse context menu to reload the current page using the library’s proxy server (to allow for off-campus access to resources which require a Caltech IP address).
Sherman Fairchild Library, 3rd floor
kbuxton AT library.caltech.edu