If you cannot log in to websites after removing the cookies associated with it, clearing your Firefox cache, and trying with your extensions and plugins disabled, you may have a corrupt cookies file in your Firefox profile folder.

• https://support.mozilla.org/en-US/kb/fix-login-issues-on-websites-require-passwords#w_remove-corrupt-cookies-file

You can check if there are entries in the password manager with an empty user name.

Make sure that you haven't saved multiple (uppercase, lowercase) versions of that name and password.

Remove currently saved Password(s) from that domain:

• Tools > Options > Security: Passwords: "Saved Passwords" > "Show Passwords"

You can remove all stored data from a specific domain via "Forget About This Site" in the right-click context menu of an history entry (Show All History or History sidebar) or via the about:permissions page.

• https://support.mozilla.org/kb/how-do-i-manage-website-permissions

Using "Forget About This Site" will remove everything like bookmarks, cookies, passwords, cache, history, and exceptions from that domain, so be cautious and if you have a password or other data from that domain that you do not want to lose then make a note of those passwords and bookmarks.
You can't recover from that "forget" unless you have a backup of the affected files.

It doesn't have any lasting effect, so if you revisit such a 'forgotten' website then data from that website will be saved once again.

Hello again, I've searched a bit till I found this link: https://bugzilla.mozilla.org/show_bug.cgi?id=800845 I got exactly the same problem, so I guess I'm gonna need an admin's assistance. This hasn't to do with my browser, any staff member please contact me, since I can't login to AMO forums in order to post.

Thanks for your replies!

Hello, I've exactly the same problem of @Scarecrow.

I can't login to addons.mozilla.org, I've tried with 2 differents accounts and with Mozilla Firefox and Google Chrome.

Both return me the same error:

"Oops! An error..."

I've tried in firefox safe mode and the problem is the same.

Can someone help me please?

Clear the cache and the cookies from sites that cause problems.

"Clear the Cache":

• Tools > Options > Advanced > Network > Cached Web Content: "Clear Now"

"Remove Cookies" from sites causing problems:

• Firefox/Tools > Options > Privacy > Cookies: "Show Cookies"

Start Firefox in Safe Mode to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance).

• Do NOT click the Reset button on the Safe mode start window or otherwise make changes.

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

I have this problem too. I just recently registered but cannot logon with my new details.