Affected versions
Nightly 81.0b5

Affected platforms
Platforms: Windows, Ubuntu, Mac OS

Preconditions
Reach about:config and set the following pref: browser.download.viewableInternally.enabledTypes = SVG,XML,PDF,WEBP,AVIF

Steps to reproduce

Launch the Firefox browser and reach https://mime.ty.ax/
From the Custom section: "File types" select the SVG file type, from the "File Extension" select by type(.svg), from the "Content-type" select by type(application/octet-stream), from the "Content-disposition" select none and then click the download link

Expected Result:
The SVG file should open directly in Firefox in the same tab.

Actual Results:
The file opens in a new tab/ window (windows/mac accordingly)

Severity suggestion
I think the severity for this issue should be an S3 since the file opens, just not in the same tab as it should

Seems like a good thing they don't as they might run script.

Isn't this a dupe of bug 1662795?

I don't see the behavior described here, though I'm confused by the steps described. "from the "Content-type" select by type(application/octet-stream)", is inconsistent, if the content type is chosen by the file type, it will never show "application/octet-stream". I think the test plan that you're referring to should instead say "by type (image/svg+xml)", in which case the expected behavior is seen, opening in the same tab, so I'll close this.

(In reply to :Gijs (he/him) from comment #2)

Isn't this a dupe of bug 1662795?

Bug 1662795 is about the missing radio button, which is present for application/octet-stream PDF.

(In reply to Adam Gashlin (he/him) [:agashlin] from comment #3)

I don't see the behavior described here, though I'm confused by the steps described. "from the "Content-type" select by type(application/octet-stream)", is inconsistent, if the content type is chosen by the file type, it will never show "application/octet-stream". I think the test plan that you're referring to should instead say "by type (image/svg+xml)", in which case the expected behavior is seen, opening in the same tab, so I'll close this.

(In reply to :Gijs (he/him) from comment #2)

Isn't this a dupe of bug 1662795?

Bug 1662795 is about the missing radio button, which is present for application/octet-stream PDF.

Right - I used application/octet-stream, ignoring the "by type" bit, and then I don't get the "open in Firefox" radio button at all, so I see the results from bug 1662795, and I don't really understand the expected results. Your explanation (that the steps should be using "by type (image/svg+xml)" makes sense of the expected results though - thanks for clarifying.