Actually, ever since Firefox 41, you may experience problems downloading files greater than 25MB if you have a slow-speed DSL connection.
There's an acknowledged bug there. So, FF 40.0.3 - despite not having the various fixes/security enhancements made up to the current v46.x release - may be necessary if you have such a connection.
The latest and greatest version of SeaMonkey works fine, they didn't alter the download manager like they apparently did in FF somewhere down the road. I keep waiting for the fix for that issue.
Opera 36 works fine with Mac OS X 10.9, 10.10 and 10.11 for the GMG site. Don't expect the WIN version would have problems?