if you donated or is affiliated with _any_ political cause, and google fired you for that reason, then they've committed illegal discrimination against you.

However, this political affiliation/activism needs to be conducted outside working hours, lest it be associated with google's official public stance or incur liabilities. You actions as an employee could be misrepresented as the position of google, and they are well within their rights to restrict how you represent yourself during office hours, and they should also be allowed to prevent you from mis-representing yourself too (i.e., you cannot use your position as an employee to act as an agent of political activism or affiliation unless authorized by the owners of google).