Hello and apologies for replying in english.
You can set the progress bar to appear in the footer by changing the progress bar position drop down menu in the editor but it is a much simpler version of the progress bar that can not contain and page or chapter markers:
Example of project with footer progress bar:
xot.xerte.org.uk/play_116
Example of project with header progress bar:
xerte.nottingham.ac.uk/play_8203
This is something that the developers have spoken about recently and we will be adding the option for the more complex progress bar on the footer too in a future release.
Thanks for letting us know about the JS you have written. You should be able to do a pull request in GitHub
github.com/thexerteproject/xerteonlinetoolkits
and then the developers can review the code and merge into the core code if appropriate. Tom (one of the other developers) can probably give more information about this if required.
Thanks
Fay