eke.
I must admit Ive not actually tried it with IE as I only really use Firefox, Chrome and Safari... although saying that Ive made changes recently using Firefox which saved perfectly fine
I have been investigating the issue with Firefox and the Zyxel modem as in my case the response from the gui has been sometimes very slow/partial screen updates or even hanging (or so it seemed).
I have reached the conclusion that Firefox is NOT the problem but my Anti-Virus Software (Avast free).
After a process of elimination removing various pieces of software running on my PC I found that disabling the 'Shields' in Avast meant that firefox worked perfectly with the Zyxel modem.
If I left the anti-virus 'shields' running I got the effect(s) as reported by kitz and worse.
I have now removed Avast completely and have installed selected parts of the Mcafee software suite as supplied by Plusnet and all is working as it should.
(Unfortunately Mcafee is aimed at an audience who prefer a 'blackbox' approach to security software and it does a lot of 'automatic' things that are not clearly reported in logs etc)
It is a great pity as I have used avast for 3+ years and it has been a good balance between functionality/usuability and minimal Interference with other software i run.
I would suggest looking at the anti-virus and/or anti-malware software you may be running as it could be interfering with firefox when accessing the Zyxel.
I do run multiple anti-virus and/or anti-malware software progs to catch as much as possible.
This could be an effect only I am seeing but I am not convinced this is the case.
I do know from past experience that you can often assume to know the general cause of a software issue only to find out later it is some s/w you least suspected to be at fault.
(Software 'side-effects' are everywhere, just not all are visible. Hence crashes and hangs still happen after all this time. Even in the world of IOS
)