I have this issue as well. The left panel in System Administrator never changes. Works just fine in Chrome, but FF is my primary browser. Happens in both FF v46 and v45.
If I go to manage a domain, the domain list remains in the left panel even though I am on the management page for a single domain. If I click on Email, File Storage, Reports, Settings, etc. the left pane never changes and only shows the list of all the domains on the server. If I click on one of those domains in the left pane, the main screen changes to the Details page of that respective domain I click on.
Any tips on resolving would be appreciated. Thanks!