VisualStudio won't accept credentials in enterprise environment

I'm currently using Visual Studio Community 2015, Version 14.0 Update 3.

My problem is, that I can't connect to my own MS TeamFoundationServer 2015 from my workplace. The problem is definitely not missing access rights, because I can connect from anywhere except my office.

I try to add my TFS using TeamExplorer -> Connect to team project -> Servers -> Add. Then I enter my connection data (which is correct, double- and triple-checked). After that, I'm asked for my credentials as seen in this picture (URL and Useame changed for the pic):

But even if I enter the correct credentials, it won't let me connect. It displays the following error:

For me, this looks like my credentials are wrong. Except they aren't. I just double checked this on a few other PCs.

The cause of the problem is probably the authentication of my company. Because if I try to open the TFS-Page in the VisualStudio browser (Ctrl + W and then W), I instantly get the following error, an usual IIS 401.

But usually I get asked for my credentials if I try to open this page, on every browser. Except on the VS-Browser.

So does VisualStudio tries to authenticate me automatically with my Windows-Credentials? If so, where can I tu this off? If not, what could be the problem?

I don't think it's because of a firewall or a proxy, because I can connect to the TFS, but just not authenticate.

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