Tom, I thought I mentioned it has the same problem when using IE as well, but at least the HTML editor shows up. Apparently people are seeing a suspiciously similar problem while using Firefox anyway. Since you're not familiar with Opera, "user mode" turns it into a dumb, open screen - in other words, if your server echos my text back, I will ABSOUTELY see it, hide commands notwithstanding. Up til last week it did~then you made changes~since then it doesn't.
I did discover that it will post my text into an auction blind as you've probably discovered, which further puts the onus on Auctiva, no? As far as trying to accomodate every browser/OS combination, any developer will tell you that OS is irrelevant, as long as it can support the browser & Java/BHO apps. Concerning browser type, there is a standards committee for such things, and if you're compliant you have the best chance of working with most, and usually all of them.
To check for compliance, you might consider pushing the listing page into this utility: http://validator.w3.org/
Try it, and you will find no less than 100 (that's a 1 with 2 zeros!!) errors. In other words, this is total sloppy code, and the only reasonable course for Auctiva at the moment is to return the site to where it was a week ago, then fix the code offline (and ask the Jolt Cola team to validate it this time?)