Firefox stores your bookmarks, saved passwords, and other useful data in a profile folder. You can locate the profile folder most easily from within Firefox, but you also can locate it using Finder. This article has more information on the profile folder: [[Profiles - Where Firefox stores your bookmarks, passwords and other user data]]. But to address the immediate issue, does the error page you're getting have an "Advanced" button that you could click? If so, please click that and copy/paste the more detailed explanation of the problem into a reply. ---- These are some more general suggestions: When you have a problem with one particular site that previously worked normally, a good "first thing to try" is clearing your Firefox cache and deleting your saved cookies for the site. (1) Clear Firefox's Cache See: [[How to clear the Firefox cache]] If you have a large hard drive, this might take a few minutes. If you do not see the number going down on the page, you can reload it using Command+r to check progress. (2) Remove the site's cookies (save any pending work first). 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. ''If you can't open View Cookies on that site because of the error, open the dialog on a different site and edit the domain that appears in the search box to the one where you have the problem.'' Then try reloading the page. Does that help?