Way way off the OP topic but...

Specifying the version in a single <script> tag doesn't seem all that big a deal to me. Load a single js file with that tag and then load all other external scripts programmatically with the XPCOM inteface @mozilla.org/moz/jssubscript-loader or something like JSAN. That way everything else loaded specifies the same version, then add your inline script attributes and/or event handlers programmatically as well.