Definitely useful but pleaseeee consider adding the option to have extension keyboard shortcuts (e.g. cmd+shift+1 to convert the selected text to uppercase) similar to the Chrome extension "Change Case" by the developer bartoszlorek.

Well, it does what it says on the tin.
But not always: for some reason not on https://freetm.com and similar websites, where it’s the only place where I would really need it for work.
I translate, and very often some long sentences are 100% the same as the previous time, but now all caps, or no more in all caps. The solution for me was to open Libreoffice Writer, paste the sentence and change the case, to copy it again and paste it where I needed.
Now I can paste in a facebook comment and change the case there. It would be grand if I could do it directly in the website.
Thanks!

PS: I couldn’t find the way of replying to you Janghou, so I deleted the previous identical review, and repasted it identical, adding this PS.
Thanks for your reply, but if you register at freetm.com, you will see that even with 2.95 version the add-on doesn’t work. As the domain itself says, it’s free.

Your response Janghou was:
Sorry to hear freetm.com does not work, unfortunately https://freetm.com is not freely accessible. I guess the sites uses some fancy JS that renders the text inaccessible for the extension.

PS2: Same as last time, I deleted my previosu review and pasted it again the same adding this bit.
Yes, freetm is free, but in any case I created an account for you, Janghou:
UserID: d1494357@urhen.com
PW: Asdf0987!
Also, it doesn’t look like to have crazy javascripts: it’s a very basic html page, with 4 js presumably for the buttons up top.

In any case, over there I uploaded a Pizza.txt file, from English to Italian.
It just says Pizza, and it has wrongly been translated as PIZZA, in all caps.
Please Janghou, try to log in, double click on Pizza.txt and then double click on the PIZZA all caps to enter the edit mode: you will see that your addon there doesn’t work.

It works great in some websites, but in some others websites (such as Firefox Addon Collections), doesn't convert my small case text into capitals. If you fix it to work in all websites with no exceptions, I will give all five stars!! :-)