For heavy users (like me) I suggest using one of many "implementations" of a auto-scihub bookmark here: https://github.com/nfahlgren/scihub_bookmark It is a great addition to an otherwise clean tor-browser...

This is not mine - but looking at the code you should notice fairly quickly that it is somehow trivial. Note also that it may be necessary to change the URL if necessary.

Lastly it should be said that sci-hub does indeed need donations - it is essentially a one-woman project and she can always use some lawyer-funds...