Thank you for reporting this problem.
I have been unable to replicate the error message, using Firefox 88.0.1 – even with all permissions blocked by NoScript and uBlock Origin. Similarly, no such message appears when using the TOR browser (which is Firefox-based) with the default paranoia settings.
If the error appears in the bottom corner and remains in the same place when you scroll the page, the culprit could be the “btt-arrow” overlay (a button marked with a caret character which facilitates fast scrolling to the top of the page). This button relies on javascript and possibly jquery.
It sounds like there is a local problem with the SSL certificates stored on your own device. One potential fix is to clear your browsing history:
- Open Firefox and click the three lines button at the top-right corner in Firefox browser.
- Next click Options -> Privacy & Security. Scroll down in the right window to find History, and click ‘Clear browsing data‘.
- Select a time range like ‘All time’ (or a more recent period if you want to retain some elements in the History list), and tick ‘all options’ under Browsing history. Click the Clear Now button to clear all browsing history on Firefox.
Then revisit the blog again to check if the error message is gone. Let us know what happens.