Out of frustration with win 10 I switched to Deepin 15.4 which someone installed for me. I am totally new to Linux.

Deepin 15.4 looks really good and seems easy to use until I have to adjust things. So, I am in a learning process and will probably come up with lots of questions...but first the most urgent issue.

I have internet banking that I access with firefox. When I try to log in I get right away a weird error message from the banksite about my systemtime being 15 minutes in the future. It is impossible to log in as it will simply refresh the loginscreen after I filled in my login data.

What is up happening here, any notions?
Thanks!

Is your system time incorrect?

What do you get if you enter the command date in the Terminal program?

(do so while also looking at a watch/clock and give us that time too)

Yes, it is correct, I have set it to synchronise online
Tuesday May 30 18:4:41 UTC 2017

Are you in the UTC time zone?

Yes, I am and I just checked an old win7 computer that can login to the banksite (also with firefox) and it is also set to the UTC time zone. So I guess that is not the problem.
Anyway, it would be bit strange if the bank was concerned with my systemtime and whereabouts in the timezones. It has to be something else...

I know, but I had to check just in case.

On the principle of swapping elements out, have you tried using another browser e.g. Opera?

Okay, I installed Opera and it gives exactly the same weird message that my systemtime is 15 minutes in the future.
However it does allow me to login without any problems...

So can I conclude that the inlogdata that I put in on the exact same bank login fields somehow do not reach the bank with Firefox? Or do reach the bank but in a distorted form which makes them refresh the screen so the input can be given again?

Ok. So there may be 2 separate problems here.

Can you now try Firefox with no addons (Safe mode)?

First close Firefox, then run

from the command line.

It makes no difference, still not able to login...

Ok, thanks, so it wasn't a Firefox extension to blame for the non-ability to log in.

The next swap-out to try would be using the same version of Firefox on another distro or operating system. Do you have one handy?

I am a bit confused here -- are you stating that the country you are in is currently at UTC? I don't mean to pry more than necessary but are you in Portugal or Africa and they've yet to add an hour or are you in somewhere like the Antarctic? I'm not sure how it would account for the error but I can't think of anywhere that is in UTC at the moment.
What usually happens between Windows and Linux is that the Windows install expects the clock to be set to local time and the Linux install expects it to be set to UTC so adds an offset. In my case that means that, currently, the system clock shows 19:02 and Windows would show this (had I not edited the register) but Linux shows 20:02.
The fifteen minutes is perplexing though unless you're using NTP and there are some issues.

Only have and old win7 computer...with latest firefox version

And you can log in successfully on that?

Yes, zero problem, also no warning on systemtime that is set in the future even though the timezone is set exactly the same...

Ok, thanks. Look, you're going to hate me for this, but I would recommend that you download another distro, e.g. Mint, and boot off live media to test whether you can log in to your site using Firefox on that. It would be useful to see if this is somehow a Deepin-related Linux problem.