Fix the https-everywhere-disabled test
Fix the https-everywhere-disabled test

Now that https-everywhere is installed as an xpi file the test fail
because we can't update the preferences.js file from the extension.
We now use the global preferences/extension-overrides.js preferences
file instead.

boklm/tbb-testsuite,boklm/tbb-testsuite,boklm/tbb-testsuite,boklm/tbb-testsuite,boklm/tbb-testsuite