Have you tried "refreshing" Firefox? Please note that it will delete your add-ons and reset all of your settings. https://support.mozilla.org/en-US/kb/refresh-firefox-reset-add-ons-and-se...

Refreshing Firefox {web link} is a LAST RESORT ! !

Refreshing Firefox -- easily fix most problems

If you're having problems with Firefox, refreshing it can help. The refresh feature fixes many issues by restoring Firefox to its factory default state while saving your essential information like bookmarks and open tabs. Everything else, like user settings and add-ons, are removed.

Make sure you are not blocking content.

Start Firefox in Safe Mode {web link} by holding down the <Shift> (Mac=Options) key, and then starting Firefox.

A small dialog should appear. Click Start In Safe Mode (not Refresh). Is the problem still there?

I fixed this by going to Firefox Preferences, Content, then Block Popups, and adding an Exception for the website that I was on. That enabled the website to open up a popup window for me to enter my credit card information and finalize the sale.

That was very good work. Well done. Please flag your last post as Solved Problem so others will know.

FredMcD said

That was very good work. Well done. Please flag your last post as Solved Problem so others will know.

Fred; I see no means to edit the post and tag it with being a solution. Sorry.