Unfortunately it is not possible to open several hotels in several tabs of the browser, because the sessions then get mixed up.
For this problem there are two possible solutions:
One can use for every hotel a different browser, eg Hotel A opens with Explorer and Hotel B with Chrome this way both hotels can be managed at the same time with no interuptions or mix ups.
Chrome has the possibility to create different user accounts (chrome :/ / settings / create profile). Meaning with Chrome You can manage more that one Hotel using different user accounts, it is then possible to open several hotels in different browser windows simultaneously.