Have you modified the Elgg core file? It could be that a plugin overrides the footer view resulting in your changes not being visible.
If you only attach your changes at the end of the core footer view, you can extend the view also by coding a little plugin. It's better to include your changes in a separate plugin anyway regardless if you extend or override the view. Put this plugin then at the bottom of your plugin list and it should work.
I havent managed to add a <script> into footer.php in views / default / page / elements / footer.php
why could that be?
how did you try to add it?
First by closing the php, adding the script and then reopening the php. A <iframe> working correctly.
it would be more helpful if you actually posted the code of what you tried, or what you want
Have you modified the Elgg core file? It could be that a plugin overrides the footer view resulting in your changes not being visible.
If you only attach your changes at the end of the core footer view, you can extend the view also by coding a little plugin. It's better to include your changes in a separate plugin anyway regardless if you extend or override the view. Put this plugin then at the bottom of your plugin list and it should work.