Just one suggestion for the Firefox addon:
I often use to bid on items in groups. It would be great, if I could add a new group via the Firefox popup window.
At the moment it is just possible to choose an existing group (added at the myibay web frontend).
This window was optimized for its small size and since adding/deleting a group is not a vital feature in such a small pop-up, you better do it in the main interface.
This way we can keep this small window in KISS principle.
I personally add groups very rare (about once per week or two), although I have about 35-40 groups.