Disable all Adobe plugins in Tools -> Add-Ons -> Plugins and click the PDF link again. It should not open the file in browser then, and it possibly would be easier to save.

You can setup the actions for Firefox to take when you open PDF links at the Applications panel in your preferences.

Maybe I did not make the problem clear. No trouble downloading, viewing or saving pdf's themselves. But I need to save some html pages as pdfs. (The UK tax office will only accept attachments online as pdfs: WHY is beyond me!!!!) Chrome has/had a print to pdf option and I think this must be how I previously saved from FF. This seems not to be there since the update to 43.

Do you have a PDF extension installed that became disabled as a result of the Firefox 43 update and the new requirement that all extensions need to be "signed" by Mozilla?

https://wiki.mozilla.org/Addons/Extension_Signing

I don't think so, unless it has been completely removed.Nothing relevant shows.

I do notice that the Adobe Acrobat pdf plugin for FF is out of date (9.5.5.316) but it has been like that for a while. I think thatthe latest may now be at 10.xxx but I don't like to update something that so far has worked fine (and Adobe can be a real pain: eg Flash).

I found another question referencing an add-on (Print Edit) and downloaded this. It seems to do what I want, though in a slightly roundabout way. I still would like to know whether print-to-pdf should be available in FF43 and if so where it did it go??!!

An old extension installed by an old Adobe program wouldn't have the "signing" that is required to be enabled in Firefox 43. That is why I asked if you had a disabled extension in the Add-ons Manager Tab which can be viewed via { Ctrl + Shft + A} from the keyboard. Firefox wouldn't remove it, only disable it.

The only items flagged as being disabled are 2 extensions: 1 Microsoft .Net Framework Assistant 2 Zone Alarm Security engine. These were both previously disabled but now have a new red flag saying they could not be verified Also there are 2 plugins which have always been disabled 1 OpenH264 video codec by Cisco 2 Windows Presentation Foundation (WPF)

I suppose it's possible that my old Adobe pdf plugin has somehow been internally disabled or is now missing an external component, but it doesn't show any visible signs and still works to show pdf files.

Does Firefox have a direct print to pdf, or does it use the Adobe plugin?

Anyway, he Print Edit extension seems to work fine and has a few useful extra features. I like it so far!

One other possibility: if you used Firefox's Refresh feature, most of your extensions would have been removed (only extensions installed by other applications are automatically rediscovered after a Refresh). The tell-tale sign is an "Old Firefox Data" folder on your desktop. Do you see anything like that?

Firefox for Windows does not include any PDF creation feature. An add-on or a PDF printer driver is always required on Windows.