[orca] Clear content cache when Thunderbird window is deactivated

[Joanmarie Diggs <joanied src gnome org>]

commit 48de4f32d71e5903599f5ebf3b7df82e4c42410b
Author: Joanmarie Diggs <jdiggs igalia com>
Date:   Thu Feb 25 01:02:27 2016 -0500

    Clear content cache when Thunderbird window is deactivated

 src/orca/scripts/apps/Thunderbird/script.py |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/src/orca/scripts/apps/Thunderbird/script.py b/src/orca/scripts/apps/Thunderbird/script.py
index 9878675..97096a3 100644
--- a/src/orca/scripts/apps/Thunderbird/script.py
+++ b/src/orca/scripts/apps/Thunderbird/script.py
@@ -461,3 +461,4 @@ class Script(Gecko.Script):
 
         super().onWindowDeactivated(event)
         self.spellcheck.deactivate()
+        self.utilities.clearContentCache()