So you are trying to open the .htm file in IE and IE hangs or you try to do it in Firefox and it hangs? Your paragraph:

When I try to open the file in Internet Explorer rather than Firefox, I get a message that JavaScript is not enabled. However, I do have JavaScript enabled, and have just updated Java to Version 7, Update 51.

gives me the assumption that you are having problems with IE instead of Fx. Can you clarify if it hangs in IE or Fx?

One possibility is something in the file is trying to use the internet.

One of the problems with saving web pages from complex dynamic sites like Gmail is that you may be saving the instructions for rendering the page rather than the actual content of the page. In that case, if you are logged out of your account or there is a cross-site security bar to pulling the needed data, then the saved page may not display correctly or at all. If a message is critical, it's a good idea to print or save the page to PDF or grab a screen shot to work around that problem.

The message you're getting in Internet Explorer may be related to the fact that IE has different security zones with different restrictions. For example, sites in the Internet Zone normally can run JavaScript, and sites in the Restricted Sites list cannot. The local computer zone has much tighter security compared with the old IE6/XP days, and that may explain what you're seeing there.

P.S. Browsers interpret JavaScript internally without using the Java plugin.