I launched Firefox. I opened a bookmark to a regularly visited web page. Firefox immediately crashed. Just abruptly stopped running and disappeared. I have visited this web site many times through the years and had done so only a day or two previously.
I tried many tricks. Nothing worked.
I created a new profile and Firefox did not crash. Slowly I rebuilt important files. All was calm.
I again created a new profile. This time I copied important files from the original profile. All was calm.
Like the proverbial deer in the headlight beam, I stared at the monitor display.
I renamed the new profile. I launched Firefox with the original profile. Firefox crashed when opening the web page. I closed Firefox and renamed the profile by changing one character. I launched Firefox. Firefox did not crash when opening the web page.
I reversed the steps to restore the original profile name. Firefox crashed.
I restored the new profile. No crashing. I renamed the profile the same as my original profiled. Firefox crashed.
I have no idea why the profile name causes Firefox to crash for this one site only. Or why this behavior started out of nowhere.