Google Calendar is not working in my browsers, how can I fix it?

Question

Browsers

The laptop has several browsers:
1) Opera, version 60.0.3255.170;
2) Firefox, version 67.0.4;
3) USBrowser, version 7.0.185.1002.
Google Calendar stopped working correctly in all browsers: the site opens, existing events are displayed, months are scrolled, but it is impossible to create a new event or edit an existing one. All entries in the calendar are perceived by browsers as plain text and clicking on them does not work, a maximum of them can be selected.
Events cannot be viewed as page elements - the right mouse button fires everywhere except in the event area. When opening the page code, there are no events in it (I searched by name - it is not in the text, although it is in the output final page).
Previously, I saw this on a working machine, but only a part of the browsers had such a problem there, and the other part worked fine.
Actually the question is what is it and how to fix it?

Answer 1

run without plugins
and without a proxy
will not help - return browsers to their initial state after installation