-> Demanding that he resign and step down and/or pressuring people to force him to resign? If that comes to pass, that he is forced out of his position against his will, then that isn't free speech at work, it's tyranny of the majority. He will have been effectively fired for his religious beliefs.
Title VII of the Civil Rights Act of 1964
Section 703(a)(1) and (2)
"(a) Employer practices
It shall be an unlawful employment practice for an employer -
(1) to fail or refuse to hire or to discharge any individual, or otherwise to discriminate against any individual with respect to his compensation, terms, conditions, or privileges of employment, because of such individual’s race, color, religion, sex, or national origin; or
(2) to limit, segregate, or classify his employees or applicants for employment in any way which would deprive or tend to deprive any individual of employment opportunities or otherwise adversely affect his status as an employee, because of such individual’s race, color, religion, sex, or national origin."
What the hell else do you (rhetorical you) need? Why is anyone suggesting that he should be forced out of his position and that he "should have known that there would be ramifications". Perhaps a shitstorm, but never unemployment. This violates the law.
It would be if Mozilla Corp (an employer) fired him or told him he must resign, hence the part "pressuring people to force him to resign". You can demand and complain all you want, but until management responds to that opinion with a loss of employment, no it is not abuse, and I would agree. Sorry if I didn't make that clear.