Hi Ilia, Not suggesting that, although I do happen to have an old Vista machine I use sometimes for which updates past Chrome 49 are unavailable. I happened to be using it to access my home lab Linux system today when I ran into the issue. (But I also have a FF browser on it that does work.) That said, in my day job I run a fairly significant commercial web site, and while newer versions of Chrome are more prominent, over 9% of traffic over the past couple of days has surprisingly come from Chrome...
I saw the same issue with 1.890 (fresh install) on Ubuntu 18.04, but only on an older version of Chrome (v49). I can navigate around and display everything but none of the action buttons work, essentially rendering Webmin unusable. Newer browser versions (Chrome 68. FF 62) seem to work for me. Not sure what version of FF the OP was using, but even FF 52 appears to work fine. In case it is helpful, on Chrome 49, I see this in the console output (console output on the other browsers I tested is clean):...