When I open a link in a pdf file downloaded by Foxfire, it uses Safari, not Foxfire, although I have designated Foxfire as my default browser

Question

When I download a pdf file with Foxfire and then click on a link therein, it calls upon Safari, not Foxfire, to get that link. This causes some complications. I have designated Foxfire as my default browser, so this should not happen. Is this a fault of Adobe or something else?
== This happened ==
A few times a week
== some time ago

Answer 1

-> 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 -> Zoom -> click "Reset" -> Page Style -> select "Basic Page Style"
-> go to View Menu -> Toolbars -> unselect All Unwanted toolbars
-> go 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 -> 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
-> Click OK on Options window
-> click the Favicon (small drop down menu icon) on Firefox SearchBar (its position is on the Right side of the Address Bar) -> 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 Extensions (Add-ons) -> Restart Firefox
You can enable your Known & Trustworthy Add-ons later. Check and tell if its working.