SOLVED: “Open with explorer” disabled in IE11

[SOLUTION]
I found that this button was disabled because of this line in my Master Page – I am using Bootstrap theme from Codeplex and that comes with its own master page.
What I had to do was change this line in the header from:
 to (taken from Seattle master page)
And now, the button is enabled and working!
 
[PROBLEM]
I have an issue with Internet Explorer 11 and SharePoint 2013. The option “Open with explorer” is disabled, it works in IE10 but not IE11:

I have tried all possible solutions:
– added the site to Compatibility View settings
– added the site in Local intranet
– checked the add-ons
– checked that the local service WebClient was started
– I am running the 32-bit version
– the kb 2846960 is installed (http://support.microsoft.com/kb/2846960)
And obviously it is working in Internet Explorer 10. Maybe there is a new hotfix or something that needs to be installed, have googled this but not found any proper solution yet.

Tasks and Timeline disabled with bootstrap in IE11

This problem ONLY concerns IE11 and on a SharePoint site using the bootstrap theme. When you create a Team Site and add a Task list, the ribbon is disabled and either the Tasks nor the Timeline is visible. If you open the same site in IE10 or Chrome, it is visible and working.
The site is added into the Compatibility View Settings and if I apply the Default Theme then it all works so it must be something in the bootstrap CSS files or JS that is blocking.