According to the plugin author, GWT Development Mode won't be supported in Firefox
27+. [1]
I suppose workarounds will be developing in Chrome, developing with Firefox 24 ESR
perhaps, or investigating GWT Super Dev Mode. [2]
[1]
https://plus.google.com/+BrianSlesinsky/posts/2ZsefAgkV8j
[2]
http://www.gwtproject.org/articles/superdevmode.html
Greg Sheremeta
Red Hat, Inc.
Sr. Software Engineer, RHEV
Cell: 919-807-1086
gshereme(a)redhat.com