Link introspection (when API key is added) breaks comments on Amazon wishlist entries by inserting HTML in comment area. No way to retroactively upload file, nor see upload history. VT file upload auth prompts are considered to originate from visited site, and thus can be subject to "Don't allow from this site" option on per-site basis, reducing security. Need, instead, to originate from extension. Causes github.com/ichaoX/ext-textFragment/issues/24 to reproduce.

They should create new vendor agnostic URN:SHA-256: protocol or similar instead of search selected hash and 5-6 actions per each hash... 1-3 clicks is clearly better than 5-6...

Used this add-on for many years. But the last version (4.0.2) breaks the CSRF check on my "postfixadmin" (3.3.11) site. After sending the login credentials I get "Invalid token! (CSRF check failed)". As soon as I disable VT4Browsers the login works again.

It consumes your daily quota of API requests very fast (yes, because even if your answer 'No' to don't scan a downloaded file)

Every time I open Firefox, it displays the welcome tab - annoying, unnecessary, inappropriate.

Terrible UX. Asks every time when uploading a file -- and after upload even, which makes no sense. Doesn't show scan result at all, only a link to it.
On the bright side, scans files themselves, too, rather than just URLs.