Start Firefox in Safe Mode {https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode} by holding down the <Shift> key (Mac = Options key), and then starting Firefox.

A small dialog should appear. Click Start In Safe Mode (not Refresh). Is the problem still there?

On a different note, I see that you are using Firefox ver46.0. Maybe you should consider updating to the latest Firefox ver53.0.3. If you update then check whether the issue still exists.

Product Firefox Release Channel release Version 46.0 Build ID 20160421124000 OS Windows 10 OS Version 10.0.15063

bp-81b49ab8-2ef0-426a-894c-84e890170605 Signature: JS::CallbackTracer::onStringEdge

https://support.mozilla.org/en-US/kb/update-firefox-latest-version?cache=no Update Firefox to the latest version 51.0.3