Multiple HTML Reply Signatures Remotely Served?

Ronald Heft of cavemonkey50.com made a comment here asking a question about how users could use their HTML signature when not at their own computer.

This question interests me because I believe that applications need to be accessible via the web. Many power users use more than one computer, and Firefox Extensions must correspond to a specific user profile.

There are ways around that within corporate networks. A Firefox Extension installed in a roaming profile will function for a user no matter what computer he or she uses, but a computer in the library or a coffee shop will effectively leave the user signatureless.

For my dual-boot setup, I could install my profile at a location on my FAT32 partition that is accessible by both operating systems. Then I could use the same centrally-configured Firefox Extensions, bookmarks, browser history, and other Firefox functionality from both Linux and Windows.

But suppose I'm sending an email from a friend's computer who is running Firefox, but who doesn't have my signature extension configured? Is there a way to serve this extension remotely? Applications such as the Mozilla Amazon Browser have made me very curious, and anyone who could implement something like this would surely differentiate themselves from the competition, as I'm not the only developer with a fancy HTML Signature extension.

As I mentioned in a previous post, I tried to manipulate the Google Docs interface so that I could use shortcut keys. Would it be possible to serve a XUL application that provided an interface to Gmail? Can another server -- perhaps one with the Greasemonkey engine installed -- effectively act as a middleman between a user and another server? Would security restrictions prevent this? Suppose I installed Firefox and the Plain Old Webserver on a remote server? Could I then serve my Firefox Extension remotely?

We will have to think about this concept for awhile...