I ran across an issue with the latest release (77.0.1) today on windows where PDF links will spawn a never ending cycle of new tabs, causing me to have to close the window completely (and sometimes even new windows will spawn in its place). I first had this happen with the "Click to enlarge" pdf link on http://www.emeraldashborer.info but also confirmed the behavior with a pdf result in duckduckgo as you can see in the video linked below.

This behavior does not exist in my synced profile on OSX, only in Windows 10, but it does not behave this way for another person in my team who is also running on Windows. I'm guessing it has something to do with a pre-existing setting I may have and the change in how PDF links are handled.

Let me know how else I can help.

https://www.dropbox.com/s/ajmrl2no4jwp7hk/2020-06-10%2010.31.04.mov?dl=0

In preferences you can set the action for PDF to Preview in Firefox or anything other than opening directly with Firefox.

I think something was done in 78 to mitigate this, but can't find anything useful.

(In reply to Francesco Lodolo [:flod] from comment #1)

In preferences you can set the action for PDF to Preview in Firefox or anything other than opening directly with Firefox.

So, my preference was set to "Use Windows default application" and in the windows 10 association it was set to Edge.

However, changing the preference to opening it directly did indeed fix the bug.. -shrug-

thanks flod!

(In reply to Francesco Lodolo [:flod] from comment #1)

In preferences you can set the action for PDF to Preview in Firefox or anything other than opening directly with Firefox.

I think something was done in 78 to mitigate this, but can't find anything useful.

Bug 1633790 was fixed in fx78