EDIT 2024:
Can't instal your addon (Corrupt)

No Change about this request?:
It should be a good alternative to "Case Changer" ...
if it can handle text on all part in the page, not only in Inputs.

Je voulais remplacer ma vieille extension Case Changer (qui n'est plus compatible avec Firefox 57.0) par celle-ci. Ça ne marche pas non plus avec Firefox 57.0 :-(
Pas moyen de changer la casse des caractères d'un mail sur le site https://mail.yahoo.com

Didn't work for me using Gmail with Firefox 55.0.2 running under Windows 10 (ugh!).

I'd been using Case Change Tool 1.0.rev44.1-signed.1-signed by Harry N without any hassles for many years but this does not work in the latest version of firefox.

I've now switched to TitleCase 3.1.1 by Joshua Pack. This does transform strings into Title Case, Proper Case, Start Case, Camel Case, Upper Case, and Lower Case. You have 2 ways to change text. Either by right clicking on the field and changing the case or by highlighting and only changing what you highlighted.