Hi missdlw,
Thanks for helping to bring this to our attention. We have just started to receive warnings of this nature when uploading images through Firefox or Chrome since the latest Java update and our technical team is currently looking into what we may be able to prevent these warnings from occurring.
We do not currently believe this warning is indicative of a legitimate security risk but, if you would prefer not to click the “Don't Block” option on the prompt, you could potentially work around the issue for now by switching to the Internet Explorer browser (with which the uploader does not use Java) or using the Basic HTML Uploader.
If you would like to update your account such that the Basic HTML Uploader is used when you upload from the listing creation page, just mouse over the “My Account” tab, select the “Acct Preferences” option under Settings, check the box next to “Use HTML Uploader on One-Page Lister” and then click the “Update Account Preferences” button below.
I will update this thread as additional information on this new warning becomes available. We apologize for any inconveniences this may be causing.
-Mike