My computer wouldn't even load the home page for me to be able to log in and I had to reinstall firefox 52 ESR again. Once I did, it loaded the home screen and I was able to log in. After that i clicked to go in (it opens another window) and it gave me the uh oh screen and that's when i typed the client thing. Seems to be fussy though and doesn't always work but works for me for the most part. I know lots of other people having this issue though. I wish you good luck if you find something that works for you, be it reinstalling, or trying another browser since Pal installation isn't working atm either.
Edit: It looks like Pal may be fixed. Simba posted earlier today about it:
May be an option for you to explore