User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/78.0.3904.87 Safari/537.36

Steps to reproduce:

Stored XSS using an SVG file

Login Bugzilla:-
1Go to bug..
2)Go to Show Attached Iamges.
https://bugzilla.mozilla.org/attachment.cgi?id=9107901&action=edit

3)Click on View with svg image id 9107901

Second XSS:-
Replace the edit parameter with t=F6qKq3qWf3AeaxvCfBxjMJ

https://bugzilla.mozilla.org/attachment.cgi?id=9107901&action=edit

https://bugzilla.mozilla.org/attachment.cgi?id=9107901&t=F6qKq3qWf3AeaxvCfBxjMJ

Actual results:

The file should be open without executing a script.

Expected results:

Successfully Executed Store XSS with SVG file.

Thanks for your report, but this behavior is by design and desirable. You'll note that the attachment domain used for attachments is variable to prevent abuse of the bugzilla.mozilla.org domain