Better error message, b=69560, r=robinf, sr=kin

editor/ui/composer/locale/en-US/editor.properties

@@ -156,7 +156,7 @@ RemoveLinksAccesskey=n
 RemoveLinks=Remove Links
 StopLinks=Discontinue Link
 #
-NoAltText=You should always supply alternative text for an image,\nbut you may use a space if you really don't want it.
+NoAltText=It is recommended that you supply alternate text that will appear in text-only browsers, and that will appear in other browsers when an image is loading or when image loading is disabled.
 NoAlignChar=No alignment character supplied.\nEnter a single character or\nselect a different alignment style.
 SaveImageAs=Save Image (%NAME%)...