For anyone running into this problem and finding this page via google, I managed to work around the issue locally. It stems from clarity.js:1123 which iterates over parent.frames. In my case, the LastPass extension had inserted a frame into the document, with a moz-extension://.... url.Disabling LastPass after login allowed me to use the web ui normally. For your own cases, you will need to sort which extension it is that is causing the issue in your browser. You should be able to do this by setting a breakpoint at the line I mentioned above, and reloading the page. Inspect the list of frames and match to your extension(s).
When using a modern browser such as Chrome 67 or Firefox 61, the OpenManage Switch Administrator Web UI on the N1100 series of switches fails to show the the main panel - only the header and left hand navigation are shown. This prevents the usage of the Web UI for viewing information or changing the configuration (i.e. it's useless!). Opening the Developer Tools in Chrome, the reason the main panel fails to load is due to a Cross-Origin Frame Access Violation. One of the loaded scripts attempts to access the main panel frame but this fails due to the violation. The script in question seems to be Clarity.js - i'm assuming (hoping) however that this is a Dell-developed script and not the Microsoft Javascript library for user profiling/telemetry on webpages which would be a very odd thing to include on a switch administrative interface! Due to this issue, It is only possible to use the Web UI via a less-secure browser that does not enforce Cross-Origin Frame protection such as IE11. The switch(es) are running the latest publicly available version of code from Dell - 6.4.2.6.  
Cross-Origin Frame Error on N1124/N1148 Web UI