Visual Studio Do not open new browser instance

when I try to run a web application in visual studio 2017RC on windows 10, it opens a new browser instance(in my case chrome). I’ve tried also with internet explorer, situation is same, and browser not signed in, but if I just manually run chrome it is signed in.
How to prevent visual studio to run a new browser instance on each time I run web application? When I press run website it should be opened in same window as previous application(just next tab)

C# 7 features don’t work within a web project on Visual Studio 2017 RC

I have several projects in the solution, and the C# 7 features, such as tuples and throw expressions, work fine in all of the library projects, but there is a (non Core) web project that doesn’t compile due to errors on the C# 7 features. Right after compiling, the error window quickly clears itself, presumably because the IDE/editor compiles the same units without error. I have to use the output window to see the compiler errors. It is as though the IDE/editor are assuming C# 7, but the compiler used in the build is not.