That's an unusual message. It may mean that Firefox is trying to send too many cookies to Adobe's site. Does it work any better to download from the following page: https://www.adobe.com/products/flashplayer/distribution3.html Scroll down to the first table and look for the line that has Mac for Safari, Firefox and Netscape Plug-In. ---- If you need to clear Adobe cookies, while viewing a page on the site, try either: * right-click (on Mac Ctrl+click) a blank area of the page and choose View Page Info > Security > "View Cookies" * (menu bar) Tools > Page Info > Security > "View Cookies" * click the padlock or "i" icon in the address bar, then the ">" button, then More Information, and finally the "View Cookies" button In the dialog that opens, the current site should be pre-filled in the search box at the top of the dialog so you can remove that site's cookies individually. Then try reloading the page and downloading again. Does that help?