FFTT said:
You can upload the photo to them and then they will provide you with a URL link to post.
This is essentially what all the majors do. I know from personal experience that on a Mac with your OS level and either FF or Safari, Photobucket, Flickr, and PBase work fine, and from reading other people's posts, ImageShack and many others work fine too. I can't imagine that Java has anything to do with anything, although if you have Javascripting turned off, you might have trouble. (although who is your "dealer?" What's a dealer?) I don't even think you need any firewall ports open except for 80, in order to be able to use these sites.
The amount of effort you put into this sounds crazy. Slow down. Don't bother trying any image format other than JPG. Pick one of Safari or Firefox, and don't bother changing browsers to try to solve this issue.
One more question I'll add to the excellent list already given is, can you provide a full path name as an example for one of your files? Occasionally, the path and file name you have will cause issues with the scripting language because of lengths and/or because of differences in handling special characters. This is rare, but it is possible.