Firefox doesn't show Roundcube correctly using https

[dr-rox]

I have a problem with https and Firefox 4 beta. When using https, Firefox shows an error in message preview pane :

File not found
Firefox can't find the file at https://example.com/mail/skins/default/watermark.html.

This is strange, because the file is on the server, also IE works fine with https. Also I noticed, that Firefox doesn't load styles instantly - I have to press refresh to get for example Settings page to show correctly. Before refresh Settings page is also garbled.

So has anyone got this problem?

[Julius Caesar]

I have the same problem with Firefox 4 beta. Especially after changing skins. I also notice that other images sometimes are not loaded as well. Clearing the cache and restarting FF seems to (temporary) solve this problem.