try : http://kb.mozillazine.org/Problems_printing_web_pages or https://support.mozilla.org/en-US/kb/fix-printing-problems-firefox

Have you tried reinstalling your printer drivers ? Please be aware that Microsoft can and will change drivers on Win 10 to their own if it feels like it. https://www.howtogeek.com/302595/how-to-stop-windows-10-from-automatically-updating-hardware-drivers/

Thunderbird Support Forum http://forums.mozillazine.org/viewforum.php?f=39

Please let us know if this solved your issue or if need further assistance.

I think I hit everything on the list. Font, margins, edited prefs.js and removed all printer lines for his print. Checked default which is the correct HP printer. I can start Edge, go to his webmail logon and print from Edge but not Firefox, Thunderbird and I installed Water Fox and no print. It is something in common wit Mozilla. He is a friend so I drove to house and tried all this rather that through Teamviewer. I'm confused. Thanks Carver

The problem then is probably in the profile maybe.

https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles

You mention this is for a friend. If you made this support question from your computer then we have some info about your cpu and not his.

If you made the report from yours please detail His OS and Version and what Firefox and Version. and list of Extensions.

Or uninstall and install from a Full Version Installer for 56.0.1 from here: https://www.mozilla.org/en-US/firefox/all/ Provided this is running FF ver 56 and Win 7 Or people are moving to the Extended Release as Microsoft is not providing enough support for Win7 and if it is a older cpu, motherboard not updated, video card not updated, chipset not updated then try https://www.mozilla.org/en-US/firefox/organizations/

Please let us know if this solved your issue or if need further assistance.

Windows 10 with latest updates, 4 GB of memory FF is 56.0.1 32 bit and I had put on the 64 bit version as a maybe solution. Did not fix To refresh, edited prefs.js offline and removed all printer stuff, put it back and it came up. Changed the font and checked page sized margins orientation. Intel processor I3 Waterfox is 55.2.2

Ctrl P on the google screen shows his printer and file/print preview does the same thing. It flashes "processing" closes and the printer does not wake up. Got to Notepad, type, Ctrl P and it prints. I have completely uninstalled and removed the printer including the folder for it. Downloaded the whole installer and and even installed as admin as I have seen HPs once in a while burp during install. Thanks Carver

so I went to my friend's house which is about 10 miles away and did a Microsoft uninstall Firefox 56 I believe, and then typed percent app data percent in the run box found Mozilla and renamed it out of the way. Installed version 55 on the computer and then it did an update to whatever with current and then I started Firefox.exe – P and created a new profile meaning not the default one. I had previously saved his bookmarks to the desktop so I reinstalled those and went to the Google screen to the control P and saw that it was his default printer. Also typed default in the Windows run box and made sure that his HP printer was the default which was. The Google screen would not print. I went up to file print preview and what I clicked print it showed same HP printer is before and would still not print. Anyone have any further thoughts? Thanks Carver

well I drove my one-way trip of 10 miles again. Uninstalled the HP office jet 6950, installed I will IOBIT uninstaller and removed all remaining pieces of the printer. Rebooted, his neighbor had loaned him a DeskJet F380 and installed that. Thunderbird and Firefox printed perfectly to the HP desk jet F380. I uninstalled the F380 made sure it was all gone, went to Windows 10 printers, had it download its whole list of printers, found the Officejet 6950 and reinstall the printer. It creates a OJ 6950 and OJ 6950 PCL-3. Making either one the default printer and nothing' prints. The 6950 prints from Edge, Internet Explorer and Windows notepad, wordpad, Libreoffice but not FF or Thunderbird. Is something getting mis-interpreted by Mozilla family? Thanks Carver

So my friend was looking for a deal and returned the other printer, OJ 6950, got an HP envy, his neighbor helped him install it and it did the same thing. He returned it and did as I had ask him and got a Brother HL2380 laser. I removed all the pieces of HP, installed the 2380 and printed from Firefox, Thunderbird and everything else and "everything" printed. So is it a HP problem or FF-TB problem? At least he is happy. Thanks Carver