Legacy plugins and new Firefox API is causing the issues. You can try finding workarounds for Firefox on legacy plugins, but they still might have some issues. Matter of the fact is until the add-on is not written in their new framework, such issues will keep happening.

Thanks for the answer. It is a pity that the problem has not been solved yet. Could you please explain what to do with legacy plugins or give a link. I could not find a solution myself.

Update: As far as I am aware, uBlock has been rewritten to the proper API. I would recommend to completely remove the extension, make sure you update your FF browser to the latest version and re-download the extension. Should solve the issue.