why cant i install any themes?
The majority of the themes say that it doesnt work with my version of firefox. Why is that? Why not have a version of firefox to work with all the themes.
Wšykne wótegrona (1)
A full theme is very complicated and needs the same rules as the built-in default theme. Any change to the default themes to reflect things like added toolbar buttons like the forget button or changes in the DOM structure will break all themes that worked with the previous Firefox version and its author need to come with an update.
There are development (beta and nightly) versions available that add-on creators can use to test their theme (and extension) if they want to make sure that their add=on keep working.