Is what you are seeing a crash report?

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

While still in Safe Mode,

Some of your crash reports weren’t sent to the Mozilla Servers.

In the address bar, type about:crashes<enter>. Note: If any reports do not have BP in front of the numbers/letters, click it and select Submit.

Using your mouse, mark the most resent 7 - 10 crash reports, and copy them. Now go to the reply box below and paste them in.

You can check if it helps to start Firefox in Safe Mode by holding down the Shift/Options key.

• https://support.mozilla.org/kb/upgrade-graphics-drivers-use-hardware-acceleration

In case you use "Clear history when Firefox closes" then try to disable this feature.

• Tools > Options > Privacy > Firefox will: "Use custom settings for history": [X] "Clear history when Firefox closes" > Settings

FredMcD and cor-el I appreciate your trouble, thank you, but I did not follow up the suggestion made in either response. I uninstalled Firefox and deleted the Firefox folder, as directed in the help pages - then reinstalled a clean copy of Firefox. This seems to have solved the problem.