TYPO3 Core

Yesterday, there was a message on slack that login fails after updating to 8.7.11. So I tried to reproduce the issue and failed, everthing worked as expected. But today I was not longer able to login again. After clicking to the login button the spinner is turning and turning and no other reaction follows. Clearing browser cache and cookies, restarting the browser or clearing T3's cache at install tool doesn't help. Tested with Firefox 59. Didn't find hints in any of the logs.

Chrome seems not to be affected, login is possible as always. I used version 64 and 65.

Request url: https://sandbox.gilbertsoft.net/typo3/index.php?ajaxID=/ajax/rsa/publickey&skipSessionUpdate=1
Request method: GET

Request headers:
Accept: */*
Accept-Encoding: gzip, deflate, br
Accept-Language: de,en-US;q=0.7,en;q=0.3
Cache-Control: no-cache
Connection: keep-alive
Cookie: be_lastLoginProvider=1433416747; be_typo_user=285ffe5a89e5a15feaade8ed158bb59c; PHPSESSID=usnut8tb5q0n5vf4odr4ad0o5g
Host: sandbox.gilbertsoft.net
Pragma: no-cache
Referer: https://sandbox.gilbertsoft.net/typo3/
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:59.0) Gecko/20100101 Firefox/59.0
X-Requested-With: XMLHttpRequest

Response headers:
HTTP/1.1 200 OK
Cache-Control: no-store, no-cache, must-revalidate
Connection: Keep-Alive
Content-Encoding: gzip
Content-Length: 311
Content-Type: text/html; charset=utf-8
Date: Wed, 14 Mar 2018 07:33:29 GMT
Expires: Thu, 19 Nov 1981 08:52:00 GMT
Keep-Alive: timeout=5, max=100
Last-Modified: Wed, 14 Mar 2018 07:33:29 GMT
Pragma: no-cache
Server: Apache/2.4.10 (Debian)
Set-Cookie: be_typo_user=e7748e8b46ddb166b726c5f5fae951ab; path=/; HttpOnly
Vary: Accept-Encoding
X-Frame-Options: SAMEORIGIN
X-JSON: true
X-UA-Compatible: IE=edge