For the author, FYI: I'm running regular Firefox on regular Windows 10. When I open your site link here and first press tab, I do not get a popup for "skip to

For the author, FYI: I'm running regular Firefox on regular Windows 10. When I open your site link here and first press tab, I do not get a popup for "skip to main content". Instead, it skips the header links entirely and jumps immediately to the hashtag section marker -- not for the first hashtag marker section at the title text, but at the next one labeled "Background". I loaded the site afresh in new tabs and this behavior repeated each time. When I navigated to the other example accesibility links you provided (such as Google and Wikipedia), the first tab press did jump first to the "jump to content" link.