Is this a problem signing into your Firefox account (to use Sync, for example), or into a website? For websites, you could try "the usual": If a site is generally known to work in Firefox, these are general suggestions to try when it stops working correctly: '''Cache and Cookies:''' When you have a problem with one particular site, 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. Then try reloading the page. Does that help? '''Testing in Firefox's Safe Mode:''' In Safe Mode, Firefox temporarily deactivates extensions, hardware acceleration, and some other advanced features to help you assess whether these are causing the problem. ''If Firefox is not running:'' Hold down the option/alt key when starting Firefox. ''If Firefox is running:'' You can restart Firefox in Safe Mode using either: * "3-bar" menu button > "?" button > Restart with Add-ons Disabled * Help menu > Restart with Add-ons Disabled and OK the restart. ''Both scenarios:'' A small dialog should appear. Click "Start in Safe Mode" (''not'' Refresh). Any improvement?