Looks like the name@domain format is indeed the recommended format for extension ids rather than GUIDs (thanks David). My bad.

Switching to scholar@chnm.gmu.edu -- SVN folks should rename the text file in their FF profile directories. (Used to be scholar@chnm, so you need to make the change even if you hadn't changed to the GUID yet.) Anyone who's tried the XPI yet will need to reinstall just once from the URL (http://chnm.gmu.edu/firefoxscholar/download/scholar-dev.xpi), as the old version won't find updates with its id.

chrome/chromeFiles/content/scholar/xpcom/scholar.js

@@ -1,5 +1,5 @@
 const SCHOLAR_CONFIG = {
-	GUID: '{e007c81c-eb2a-4e1d-b381-d25a45cd11ed}',
+	GUID: 'scholar@chnm.gmu.edu',
 	DB_FILE: 'scholar.sqlite',
 	DB_VERSION: 10, // must match version at top of schema.sql
 	DB_REBUILD: false, // erase DB and recreate from schema

install.rdf

@@ -4,7 +4,7 @@
 
   <Description about="urn:mozilla:install-manifest">
   
-    <em:id>{e007c81c-eb2a-4e1d-b381-d25a45cd11ed}</em:id>
+    <em:id>scholar@chnm.gmu.edu</em:id>
     <em:name>Firefox Scholar</em:name>
     <em:version>0.1pre1-SVN</em:version>
     <em:description>This is a one-line description of Firefox Scholar.</em:description>

update.rdf

@@ -2,7 +2,7 @@
 <RDF:RDF xmlns:RDF="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
          xmlns="http://www.mozilla.org/2004/em-rdf#">
 <!-- Firefox Scholar Extension -->
-<RDF:Description about="urn:mozilla:extension:{e007c81c-eb2a-4e1d-b381-d25a45cd11ed}">
+<RDF:Description about="urn:mozilla:extension:scholar@chnm.gmu.edu">
   <updates>
     <RDF:Seq>
       <RDF:li>