When a visitor comes to your site and clicks to post a comment, a popup window opens up.This may be annoying for users specially with slow internet speeds,So they may find a reason to dislike your site.You can avoid such mishaps like this by changing the commenting style to a comment form.It's not very though and is one of the options that blogger provides you.
Enabling comment forms:

• Go to your dasboard
• Click on the settings button of the blog you want to edit
• Go to the comments section
• Change the 'comment form placement' to 'embedded below post
• Save settings and preview any post