Affected versions

• Latest Nightly 78.0a1

Affected platforms

• macOS 10.15.5 beta 3
• Windows 10 64bit
• Ubuntu 18.04 64bit

Steps to reproduce

1. Open latest Nightly
2. Open a pdf in a tab (eg: http://www.africau.edu/images/default/sample.pdf)
3. In a new tab visit about:preferences
4. Change the Action of pdf Content Type to Always Ask
5. Revisit the first tab where the pdf is loaded and refresh the page (remember the save options)
6. Open a new tab and load the same pdf from step 2

Expected result

• Open in Nightly option is available in all tabs

Actual result

• Open in Nightly option is not available in already opened files from other tabs.

Regression range

• This is not a regression since it also reproduces on the first build where this was enabled for the first time (bug 1638682)

Additional notes

• Screencast attached showing the issue
• I am not sure if this is actually the correct behavior and the content from the tab that's already opened does not qualify as Unknown Content type.

Here i've attached the difference between the two dialogues. Existing tab | new tab

This is intentional, since it makes no sense to "Open with Nightly" when you're already in pdf.js.