I wish someone would tick the solves for this for this PDF stuff. This is about 50 times so far.

Thunderbird 91 opens PDF files in a tab in Thunderbird. Is the tab not appearing?

The tab is not appearing. When I left click on the PDF document nothing happens. I then right click an Open, Save as, Detach and Delete appears, when I click on Open nothing happens..However, if I forward the email and attachment (before sending to anyone) I can left click on the PDF and the document will open. There is not a tab opening on the document to be forwarded.

I'm having this problem--but in my case the tab DOES open -- it's just blank. I've tried it with multiple PDF attachments -- and none of them opens in Thunderbird--but they all work in Acrobat.

1) Go to: Tools > Preferences and page down to 'Files and Attachments' and make sure you select 'Use Adobe Acrobat Reader' for the method to open PDFs. Note: This did not completely solve the problem for me, so:

2) Double-click on the file in the email attachments and you will likely get a pop up that asks how you want to open the file as: 'What should Thunderbird do with this file?' Select 'Open with' and make sure that the box 'Do this automatically for files like this from now on' is checked. Then, open the drop down menu beside 'Open with' and choose 'other'. You will get a new pop up with possible programs to open the file - choose 'browse' and physically navigate to the folder on your hard drive that holds programs, then go to the Adobe reader folder as: Program Files>Adobe>Acrobat Reader DC>Reader> physically select AcroRd32 and then click 'open'.

Completing both of these steps solved the problem for me. You can complete the same process for other file types Word, Excel, etc, selecting the appropriate programs on your hard drive for those file types.

Since the October 6 update ALL attached files bring the "What should Firefox/Thunderbird do with this file" even though the defaults are set in the options of both sets of software and the "Do this automatically..." is already checked. This applies to Jpeg, Mov1, MP4 and pdf files.

Annoying. Win 7 Pro 64bit.