Just in case others have had the same issues, here’s how I solved my problems with Firefox on the Macintosh and Blogger:
For months and months, I was having problems with Blogger and Firefox, even though the Blogger people kept saying that Firefox was the preferred browser on the Mac. I had tried everything (I thought): resetting the preferences, turning stuff off and on, re-installing the software, you name it. So last night, I did a search on my laptop for “Firefox” and I discovered a couple of different sets of preference files for Firefox. I threw all that stuff away, went to the Mozilla site, downloaded and installed a “clean” version of Firefox, and now everything works hunky-dory. Now I can use the Blogger spell-checker and HTML composer feature. Life is good.
And now I can also spread the word on Firefox….