Can you expand on what you mean by "it used to be okay but has gone wrong". That's super vague and doesn't give us much to go on. An expanded description of the problem along with screenshot(s) would be helpful.

Thanks for your reply Jonathan. I will explain. It showed a print preview of the Brother Label Printer instead of the main Brother printer A4 size. The only thing that had changed in the last few days I thought was perhaps an add-on so I have deleted them all so I am not really sure which one was the culprit as the print preview problem has now been resolved.

Ah, that sounds like a known bug related to label printers that occurred in firefox 82.0, although the behavior here sounds a little different. You hopefully should be able to fix it by updating to Firefox 82.0.2, opening the page `about:config`, typing in "print_paper" and deleting all the shown preferences for the affected printer(s). Let us know if that doesn't work for you.

Another thing you can try is again to open `about:config`, then toggle the 'print.tab_modal.enabled' preference to 'true'. That should give you the (not yet released) new printing interface that we're working on the next time you try to print. The new interface may work well for you and will give you an easier option to change printers in the preview.

How to print web pages in Firefox has information about the new print preview interface that is enabled for a limited number of Firefox 82 users for testing. You can check the Troubleshooting Information (about:support) page under the Experimental Features section, to see if the Print Preview Redesign (print.tab_modal.enabled) preference is enabled or disabled in your version of Firefox.

Oh, I see that you reported a couple of hours ago the problem is now resolved.

Thanks for your replies Alice. I just deleted 3 x add ons and the print preview was fine then so I do not know which one caused this problem. I will try Jonathan's suggestion though

Iteresting. What are the names of the three add-ons? It would be good for us to be aware of which add-ons may cause printing problems.

Even more strange as I turned the add-ons back on one at a time to see which one caused the issue but the Print Preview in 'File' is working fine again. It was happening when I tried to print an order I had paid for on EBay so could the error have been caused by that website do you think?

It's hard to say. It's possible, but I'd lean towards the 80.0 bug as the most likely culprit if I had to pick. Still, the most important thing is that the issue is resolved for you. :-)

Dear Jonathan,

I have just followed your instructions dated 11/4/20 2.16 am above but if I follow the second paragraph and toggle 'print.tab_modal.enabled' preference to true I do not get a 'Print Preview' choice when I try to print? I have therefore reverted it to false