Developer reply by mikhail_s
Rated 5 out of 5 stars
Firefox 34 is more careful with how XBL bindings are applied to untrusted content (see Bug 1050049 in Bugzilla). The way to make this add-on work again is actually pretty straightforward: add an attribute: bindToUntrustedContent="true" to the [binding] element in the chrome/content/focusregainer.xml file inside the XPI.
I don't use the non-lite version of the add-on, but probably the fix will be the same there.
fixed in version 0.7
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