See if either of these support articles help.

https://support.mozilla.com/en-US/kb/Using+the+Adobe+Reader+plugin+with+Firefox

https://support.mozilla.com/en-US/kb/Opening+PDF+files+within+Firefox

I have made all changes in the articles with no change to the problem. I can download the files using IE.

-> Tap ALT key or press F10 to show the Menu Bar

-> go to Help Menu -> select Restart with Add-ons Disabled

Firefox will close then it will open up with just basic Firefox. Now do this:

-> Update ALL your Firefox Plug-ins https://www.mozilla.com/en-US/plugincheck/

-> go to View Menu -> Toolbars -> unselect All Unwanted/Incompatible Toolbars

-> go to Tools Menu -> Clear Recent History -> Time range to clear: select "EVERYTHING" -> click Details (small arrow) button -> place Checkmarks on Cookies, Cache -> click Clear Now

-> go to Tools Menu -> Options -> Content -> place Checkmarks on:

1) Block Pop-up windows 2) Load images automatically 3) Enable JavaScript

-> go to Tools Menu -> Options -> Privacy -> History section -> Firefox will: select "Remember History"

-> go to Tools Menu -> Options -> Security -> place Checkmarks on:

1) Warn me when sites try to install add-ons 2) Block reported attack sites 3) Block reported web forgeries 4) Remember Passwords for sites

-> go to Tools Menu -> Options -> Advanced -> Network -> Offline Storage (Cache): click Clear Now button

-> Click OK on Options window

-> click the Favicon on SearchBar -> click Manage Search Engines -> select all Unwanted Search Engines and click Remove -> click OK

-> go to Tools Menu -> Add-ons -> Extensions section -> REMOVE All Unwanted/Suspicious/Incompatible Extensions (Add-ons)

-> go to Tools Menu -> Add-ons -> Appearance section -> REMOVE All Unwanted/Suspicious/Incompatible Themes (Persona)

-> Restart Firefox

You can enable your Known & Trustworthy Add-ons and Themes later. Check and tell if its working.

I just looked at that site. They are sending PDF forms without an extension added to the filenames. That could be why you are having a problem. I was able to download them, add the extension .pdf to them, and open them with a PDF reader. Does Windows 7 refuse to download files with no extensions? I have no way of telling that, because I use Macs.

Have tried all suggestions from mha007 - all settings were set to these already - still no change. Maybe finitarry is correct but why does IE work?