Getting the picture right in deal submission

For IE on PC, the directions are exactly the same as what you've written for Firefox.

On Mac, there's no right click button, so you would use CTRL + click.
For Safari you would CTRL + click on the image and choose "open image in new tab" (or "open image in new window"). If you like it, you would CTRL + click on the image to choose "copy image address" and go back to your deal submission to paste it.
For Firefox on Mac, the directions are the same as your PC Firefox directions, except that you need the CTRL + click combination for the right-click action.
Find the image you like and CTRL + click on it to bring up a menu with the "view image" choice, and then CTRL + click on the image for a menu with the choice to "copy image location." Paste into deal submission.

I dug this up from an old email I sent to someone having issues with images during deal submission:

Firefox

Go to the product page, right click on the product image and select 'Properties' menu item. Properties dialog box will open. Copy the 'Location' attribute in the 'Image Properties' section and paste it to the 'Image URL' field in the Buxr screen where you pick the image.

Internet Explorer

Go to the product page, right click on the product image and select 'Properties' menu item. Properties dialog will open. Copy the 'Address (URL)' field and paste it to the 'Image URL' field in the Buxr screen where you pick the image.

Safari

Go to the product page, right click on the product image and select 'Copy Image Address'. Paste it to the 'Image URL' field in the Buxr screen where you pick the image.

PS. I re-titled your topic to sound more informative

Do you want to just add "for Mac, substitute CTRL + click for right-click" instead of repeating all the directions again? They're otherwise pretty much the same, although Mac users probably already know this.