If you think they are PDF forms, I suggest switching from the built-in PDF viewer to Adobe's PDF plug-in if you haven't already tried that.

This article has the steps: View PDF files using Firefox’s built-in viewer.

Any difference?

Sorry for the misunderstanding. It is not pdfs that cause the problem. I think the sites that casue problems are using Flash or similar to create input fields and display data.

Please post the link you are having trouble with.

This is the most common variation of the problem. https://familysearch.org/search/record/results?count=20&query=%2Bgivenname%3Awilliam~%20%2Bsurname%3Awestwood~%20%2Brecord_country%3AEngland%20%2Brecord_subcountry%3AEngland%2CStaffordshire&birth_year1=1800~1830 On the left are some filters that only seem to allow one selection that cannot be removed or a lower level selected. They work fine in IE. On other sites I have had problems entering data in forms. I can't remember which but they were mainstream sites with sophisticated web.

Fire IE (FireIE, Enhanced IE) {web link} Embeds Internet Explorer(IE) to use the powerful Firefox add-ons. Not only an enhanced IE Tab, but also an enhanced Internet Explorer with Adblock Plus and FireGestures support. Switch to the IE engine in one click and dismiss your IE.

It seams to work for me. Is this what you get ?

It's possible that one of your ad blockers or privacy-related extensions is affecting the page. One way to rule out possible interference by extensions is to test the page in Firefox's Safe Mode. That's a standard diagnostic tool to deactivate extensions and some advanced features of Firefox. More info: Diagnose Firefox issues using Troubleshoot Mode.

You can restart Firefox in Safe Mode using either:

• "3-bar" menu button > "?" button > Restart with Add-ons Disabled
• Help menu > Restart with Add-ons Disabled

Not all add-ons are disabled: Flash and other plugins still run

After Firefox shuts down, a small dialog should appear. Click "Start in Safe Mode" (not Reset).

Any difference?

Problem disappears in safe mode and (this may be my imagination) the response and rendering time has speeded up. "Security" Add-ons are AdBlock plus 2.6.6 Ads Removal 1.0.0 Advance System Care Surfing Protection 1.0.0. Ghostery 5.4.1 AVG site safety plugin 18.0.5.292

Thanks

Some added toolbar and anti-virus add-ons are known to cause Firefox issues. Disable All of them.

Do you have any suggestions which add-ons are known to cause this type of problem. I am very reluctant to disable any security feature and I don't want to switch to IE.

I haven't tried it recently, but I think Ghostery can show you a list of what it is blocking and may let you unblock them. Can you find a toolbar button or in-page icon for that?

Adblock Plus is pretty comprehensive, so Ads Removal may be unnecessary and I would try disabling that one in general.

I disabled Ads Removal with no change. Ghostery was blocking 4 sites so I tried unblocking them in turn. Problem seems to be caused by Adobe Tagmanager being blocked.I will try running for a few days with Tagmanager unblocked.

Thanks