Yes, I can confirm that after following the instructions in the bug report, upload now also works with Firefox.
For other interested, to make Firefox on Windows work with Share Upload over SSL, you first have to use Internet Explorer, add the site to Trusted Sites and download the certificate. After you have done that Firefox also works with Share upload. This is because Flash use the security settings from IE, not FF.
PS. What puzzles me a bit is why it works over SSL using proxy_jk, but not proxy_ajk.