Can I safely download older browsers and use?

Can I safely download older versions of Google Chrome and Firefox to use on OS X El Capitan?
I am applying for a job and their forums keep on crashing. The specify to use specific browser versions.
Thanks for your help.

Up to a point. The older you get, the more likely it won't run.
Tried Safari on these sites?

You pretty much need to determine what the minimum browser version is for each browser app that works with El Capitan. Then you know what older versions are safe to use. Of course beware. The newer your OS version…more than likely the fewer older browser options you have.

- Nick