The 
button 'Emulate User' feature located on the Users Grid allows Grid allows an Administrator to see the 'Permissions' and 'Roles' assigned to different Users. Utilizing multiple browser tabs while Emulating can cause issues with any tabs opened before Emulation began. Emulation can cause unexpected behavior because all open tabs in a single browser share the same login session. This limitation exists because of how browsers handle session information. If there is a conflict between Permissions or application access between tabs, the Emulator may see an 'Oops' Error.
There are two methods that PCR recommends to avoid seeing these problems / errors.
...
When Emulating another User, any additional browser tabs open before the emulation was started will need to be refreshed before they can be used. Refreshing a tab will load the tab with its current Permissions (in this case the Emulated ones). The browser tabs need to be refreshed so the current User Permissions and User data are valid for the tab. If the Emulated User does not have access to a section of the application and the section is loaded in the current tab when the Emulated Permissions load in, the User may see a message that says 'You do not have permission to view this.'.
Multiple Browsers
If you want to Emulate a User, but also use the application as your own userworking in an Emulated mode and in a non-emulated user environment is what is desired, another option is to to use a second browser for running the application as an Emulated User. When using multiple browsers, for example Firefox and Chrome, there is no sharing of session data and the User can more easily control the work space. For example, if the User normally accesses PCR-360 with Firefox, it can be helpful to open PCR-360 in Chrome. If you log into the application and Emulate the user in By logging in and 'Emulate User' from Chrome, there is no conflicting session data. Using private browsing mode in your browser will work similarly to using another browser.
...