Firefox, sidebar issue, the last link is not accessible due to "show/hide sidebar" button

[UrvishSSPL]

I'm having this issue in Firefox (I'm using version 53.0.3 32-bit).
The last link in sidebar is not accessible, as the show/hide sidebar button covers entire view.

This works properly in google chrome.

In the attached image, you can see the link labelled "Create new sidebar?"(which is having the issue)