At the bottom of my previous post, I mentioned my editing icons that are supposed to be displayed in a row just above the composing window (the one I'm typing in) had all disappeared. I suspected it was a problem caused by a Windows update that happened yesterday morning.
I found the problem after thrashing around in the Blogger Help Group and not finding a direct answer. Now I don't know if the problem is directly related to the Windows update, but since the problem is fixed, I'm not going to keep looking to find out if that truly was the problem.
Here's what worked for me:
Someone in one of the Help Group posts mentioned "third party blockers" so I decided to see if AdBlockPlus might be the culprit. I went into ABP's Options and did a search for "blogger" and found this entry:
I unchecked it and restarted Firefox. I opened up a new blog post window and the icons are back.
I'm really glad I'll be able to blog in Firefox again!