I've even went and created complete clean profile - still same error. This is kinda annoying and forces me to uses other browser for payments :/

No problem with paypal with FF, Chrome, IE or Edge. Did you try the other browser before posting about the issue here?

Separate Security Issue: Update your Flash Player or remove it using these links; http://helpx.adobe.com/flash-player/kb/uninstall-flash-player-windows.html Uninstall Flash Player | Windows http://helpx.adobe.com/flash-player/kb/uninstall-flash-player-mac-os.html Uninstall Flash Player | Mac

Note: Windows users should download the ActiveX for Internet Explorer. and the plugin for Plugin-based browsers (like Firefox).

Note: Windows 8 and Windows 10 have built-in flash players and Adobe will cause a conflict. Install the plugin only. Not the ActiveX.

Flash Player Version: Version 29.0.0.113

https://get.adobe.com/flashplayer/ Direct link scans current system and browser Note: Other software is offered in the download. <Windows Only>

https://get.adobe.com/flashplayer/otherversions/ Step 1: Select Operating System Step 2: Select A Version (Firefox, Win IE . . . .) Note: Other software is offered in the download. <Windows Only> +++++++++++++++++++ See if there are updates for your graphics drivers https://support.mozilla.org/en-US/kb/upgrade-graphics-drivers-use-hardware-acceleration

Many site issues can be caused by corrupt cookies or cache.

• Clear the Cache and

• Remove Cookies

Warning ! ! This will log you out of sites you're logged in to. You may also lose any settings for that website.

Type about:preferences<enter> in the address bar.

• Cookies; Select Privacy. Under History, select

Firefox will Use Custom Settings. Press the button on the right side called Show Cookies. Use the search bar to look for the site. Note; There may be more than one entry. Remove All of them.

• Cache; Select Advanced > Network.

[v57+] Select Privacy. Across from Cached Web Content, Press Clear Now.

If there is still a problem, Start Firefox in Safe Mode {web link} by holding down the <Shift> (Mac=Options) key, and then starting Firefox.

A small dialog should appear. Click Start In Safe Mode (not Refresh). Is the problem still there?

While you are in Safe Mode;

Try disabling graphics hardware acceleration in Firefox. Since this feature was added to Firefox it has gradually improved but there are still a few glitches.

How to disable Hardware Acceleration {web link}

OK, a short summary:

• clearing cookies and cache doesn't make *ANY* sense as I created completely new profile (which doesn't have any cookies…) and it didn't work!
• Other browsers worked just fine with same password (I had to use them to use paypal…).
• Paypal wasn't working with Firefox Developer edition neither (yet another different profile)!

And today - I tried to use other browser and it nudged me to change the password, and after I changed it the new password worked in Firefox.

I'm utterly confused…

Hmm. It might have been something wrong with the password Firefox had.

As long as the problem is gone, Please flag your last post as Solved Problem so others will know.

Hmm, not really - I was typing (well, copy-pasting) the same string!

Well, it works so the case closed, but it's still interesting/curious/interesting

FUN! Some time has passed, I had to buy something on paypal (haven't used it since march) and... obviously it doesn't let me log-in. I opened safari and voila - logged in without a problem. It also worked in Firefox DevEdition (60.x)...

A post was flagged as Solved Problem. If the problem is not solved, please remove that flag. If you don’t, others that can help may not read this post.

Go to that message, and use the Undo link to its right.

https://support.mozilla.org/kb/Clear+Recent+History#w_how-do-i-remove-a-single-website-from-my-history

Remove History For One Site

Open the History Manager <Control><Shift> H. In the search bar, enter the name of the site. Right-click on one of the listings and select Forget About This Site. This should remove all information, including any passwords / settings.

I undid the solved problem.

I "forgot the site" and it still doesn't let me in...

Some time ago, I had told you to try Firefox Save Mode. Your posts do not say you had tried this yet.

I said: "I created completely new profile (which doesn't have any cookies…) and it didn't work! " which, I would say, is far better than "safe mode". Basically vanilla, pristine Firefox doesn't let me log-in (Stable version, seems to work in Nightly, but then again - it worked in Stable version after couple of days o_O)

https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode

Safe Mode is a troubleshooting mode that temporarily turns off hardware acceleration, resets some settings, and disables add-ons (extensions and themes). If the problem goes away, that tells us one thing. If it does not, that tells us something else.

I've tried safe mode - same problem...

I called for more help.