You have NVidia’s network access manager or Forceware Network Manager software installed. Disable / remove it. https://support.mozilla.org/en-US/kb/connectivity-crashing-firefox-43-update

Start Firefox in Safe Mode {web Link} by holding down the <Shift>
(Mac=Options) key, and then starting Firefox. Is the problem still there?

THank you for your answer! I am not tech savvy and do not really know how to do this. I should specify that the links in other gmails do open and the problem seems to be only with this site. Is it possible that the problem originates with this particular site?

Without seeing the message myself, I can only guess.

See if you can post a screen shot of that part of the message.

Taking a Screen shot; Windows > Start > search box > Snip. Select Snipping Tool.

Save the picture(s) to your desktop. Now look at the Reply box below. Press the button under it that says Browse. Now select the screen shot(s) from the desktop and load them one at a time.

Again, thank you for your advice. It appears that the website announced that is doing maintenance, and I imagine this is what the problem is. I will wait until they are done with maintenance and try again. It is very generous of you to offer help -- thank you!

Glad to help. Safe Surfing.

Please flag your last post as Solved Problem so others will know.