Install FireFox 35 on Mac El Captain (OS 10) for Selenium tests

I need to write selenium tests.

My Mac version is El caption. Selenium supports up to FireFox 35.

However, when I download the 35 version fromhere as recommended in other forums, I get the error message from OSx:

“Firefox” is damaged and can’t be opened. You should move it to the Trash.

Any suggestion? Finally, I need to run selenium tests on OSx 10