Thanks again for taking this forward Ex_Brit.
I found an old version of SA & installed it for Internet Explorer 7. The icon is back on the menu bar, though I doubt it will stay there long.
I wanted to uninstall SA as a Firefox add-on, just to see what would happen if I reinstalled it. But both the "Uninstall" & "Options" buttons were greyed-out. All I could do was enable & disenable it. When I next went online with Firefox, however, I found SA was not working at all. No button, no colour-coding or highlighting of search results. And yet it was (apparently) enabled. I've toggled between enabled and disenabled but no difference. When I try to check for updates to SA within Firefox, I'm told I already have the latest version.
Probably it would be possible to get out of this loop by creating a new profile in Firefox, but I'm relatively new to FF & don't fancy messing around with it unless it's really necessary.
I've submitted a feedback report on the issue as you suggested. Fingers crossed!