Instead of marking Questions as favorite, can I mark specific answers as favorite?
This would help me to keep all my favorite tweaks/tricks/solutions at one place (favorite tab)
No it is not possible to favorite an answer in SE. You can only favorite a question.
Maybe you can change this to a feature request, though I doubt it'll be accepted or implemented in the near future.
Meanwhile however, you can bookmark or save a link to the answer you wish to favorite in your own browser.