Problem: after modifying a filter, while the URL changes, the back button is still disabled and clicking it does not restore the prior filter settings

Steps to reproduce:

1. at http://test.wikipedia.org/wiki/Special:Preferences enable new recent changes filters
2. in a new tab open http://test.wikipedia.org/wiki/Special:RecentChanges
3. modify any filter (for example hide logged in users)
4. the URL changes but the back button is still disabled

Expected results: the Back button works. When clicked once it comes back to the old setting (the logged in users are shown again)

Proposed implementation: https://developer.mozilla.org/en-US/docs/Web/API/History_API#The_pushState()_method