browser continues to change my chosen Red color back to gray

That sounds like Firefox is switching back to the default theme rather than actually saving your color choice. I’d check Settings → General → Language and Appearance → Website appearance and also check Extensions and Themes to make sure another theme is not overriding it.

If it keeps changing back to gray after that, I’d try switching to another theme, restarting Firefox, and then selecting the red one again.

I changed to another red theme but same issue. Gray replaces red theme even when I use another red theme. Not sure what else to do now? Ap[pecoate any help.