It's because the site doesn't have a page to display for that URL.
http://en.wikipedia.org/wiki/HTTP_404
Firefox settings should save themselves. You shouldn't have to do anything to make them default.
If you delete your profile (see- http://support.mozilla.com/en-US/kb/Profiles#How_to_find_your_profile -), all settings (and everything else about Firefox) will revert to like when it was new.Answer 2To run Firefox in it's default settings, close Firefox, and then, from the Start menu, go to All Programs, and then the Mozilla Firefox folder. From there select Mozilla Firefox (Safe Mode).A dialog box will open, saying you're in Safe Mode, that custom settings, themes and extensions are disabled. You're also given the option to permanently disable add-ons and bookmarks, and reset other settings or options.
Settings tab, security
You need to go to the trash or recycle bin and get them out of there. Fix your settings like you had them before
Go to document and settings, select program files, choose mozilia firefox, then extensions. Select all contents and delete them all. Exit firefox. Turn on firefox again, the red menuitem and grey area disappear. Go to document and settings, select program files, choose mozilia firefox, then extensions. Select all contents and delete them all. Exit firefox. Turn on firefox again, the red menuitem and grey area disappear. Go to document and settings, select program files, choose mozilia firefox, then extensions. Select all contents and delete them all. Exit firefox. Turn on firefox again, the red menuitem and grey area disappear. Go to document and settings, select program files, choose mozilia firefox, then extensions. Select all contents and delete them all. Exit firefox. Turn on firefox again, the red menuitem and grey area disappear. Go to document and settings, select program files, choose mozilia firefox, then extensions. Select all contents and delete them all. Exit firefox. Turn on firefox again, the red menuitem and grey area disappear. Go to document and settings, select program files, choose mozilia firefox, then extensions. Select all contents and delete them all. Exit firefox. Turn on firefox again, the red menuitem and grey area disappear. Go to document and settings, select program files, choose mozilia firefox, then extensions. Select all contents and delete them all. Exit firefox. Turn on firefox again, the red menuitem and grey area disappear. Go to document and settings, select program files, choose mozilia firefox, then extensions. Select all contents and delete them all. Exit firefox. Turn on firefox again, the red menuitem and grey area disappear. Go to document and settings, select program files, choose mozilia firefox, then extensions. Select all contents and delete them all. Exit firefox. Turn on firefox again, the red menuitem and grey area disappear. Go to document and settings, select program files, choose mozilia firefox, then extensions. Select all contents and delete them all. Exit firefox. Turn on firefox again, the red menuitem and grey area disappear. Go to document and settings, select program files, choose mozilia firefox, then extensions. Select all contents and delete them all. Exit firefox. Turn on firefox again, the red menuitem and grey area disappear.
If you uninstall Firefox and do not check the box that reads "Remove my Firefox personal data" then your bookmarks (and other Firefox settings) will be preserved because they are kept in your Profile Folder which is saved in a different location than your Firefox installation folder is so if you reinstall Firefox or update it, your previous bookmarks (and other Firefox settings) will all be intact.If you plan on reformatting your computer you must backup your Firefox bookmarks and settings to an external location such as to a USB drive, a CD, external hard drive, or use an online bookmarking service.Most online bookmarking services allow you to import your Firefox bookmarks and there some that offer automatic bookmarks synchronization between their service and your Firefox.
One will have to go into their settings on their Mozilla FireFox browser to unblock YouTube. Once in the settings go to blocked sites and remove it from that list. That should clear up the problem. If it doesn't, one may need to completely uninstall and re-install Firefox.
simply uninstall it but when it ask you if you want to keep settings and customization say yes
If you are not able to access the Tumblr custom page thing, be sure to make sure all components on your system are up to date. If it only says standard and Google Chrome and Firefox will not allow you to get into it, there could be an issue with your settings. You can also try to access Tumblr through Internet Explorer.
It is not possible to recover deleted browser history using Firefox. However, it is possible to set the history to never be deleted in the browser settings menu.
Found on Firefox help and support page: By entering about:config in Firefox address bar, user can set hidden/internal settings of Firefox. Set view_source.editor.external to true. Set view_source.editor.path to your target source editor, example: "C:\PATH\YOU_SELECTED_EDITOR.EXE"
Some trojans may mess with Firefox and IE proxy settings. Alos, make sure your firewall is configured to allow then access.