Image Upload using Flash is not working in Firefox. It works in IE and Chrome on the same system.
The usual error "ssl error invalid or self-signed certificate" appears. I tried to debug it with Fiddler, but there is either no request made at all, or a HTTP CONNECT is shown but no data sent.
I tried on different sites, all Magento 1.9+ (one 126.96.36.199), with different Certificates (from StartSSL and Comodo). The problem is on all of them with Firefox 40 and 41.0b8 an OS X and Windows. Flash Player version is "188.8.131.52" on all devices.
On all of this devices, the Upload works with Chrome and IE/Safari.
The Qualys SSL Test gives A or A+ for all sites.