I see! I was assuming this was for Marketing Email - my apologies. This is for 1:1 email templates.
In testing this out in the Template editor, I have the functionality to highlight and edit the text as mentioned earlier. I am also on Chrome, so I would assume this is an issue that is unrelated to browser.
If you have access to HubSpot Support I would recommend reaching out to them as they may be able to look at this in more detail for your particular account.