You could try this:

1. In the Location bar / address bar, type about:config and press Enter
2. Accept the warning
3. In the Search field on top, type printer
4. View any bold preferences, as well as the column that says Status and its corresponding values called user - Chances are you only see bold preferences, all followed by user (but not necessarily)
5. Richt-click all bold preferences followed by user in the Status column and select Reset
6. Restart Firefox and check whether you can print - Firefox may need a few seconds to set the new preferences before it does

Does this help?

Thanks for your reply. I have tried doing this a couple of times but so far without any luck. Any further suggestions?

I forgot to mention there is a support article offering more options besides this one. Did or could you look at it and follow the steps, especially with regard to a "full reset"? By the way, does the issue also occur when setting e.g. the Document Writer type or other printer if you have any? And what happens if you choose Print Preview?

If nothing helps or beforehand, you could take a look at this question. Basically the other suggestions given there are to try with add-ons disabled (Safe Mode - use the Help menu or hold down Shift when starting Firefox), and to scan your system for malware.

If that doesn’t help, have a look at this page to see if anything may be of help. Let us know how things work out.