Javascript issue on xwiki 8.4.4 and FF 52.3.0

Hello,

I use Firefox ESR 52.3.0 (64 bits on Debian stable and an http proxy to use xwiki behind Apache reverse proxy (for https ) on same server with xwiki 8.4.4/Tomcat 8.5.11 and probably another reverse reverse proxy (that I can not administer).

Very often I can not open pages with CKEditor, I have this error (displayed by FireBug)

Error: Load timeout for modules: ckeditor
http://requirejs.org/docs/errors.html#timeout
https://iwiki.din.developpement-durable.gouv.fr/webjars/wiki%3Axwiki/requirejs/2.2.0/require.min.js?r=1
Line 7

I have not this error in Chrome anyway on same PC but I want to debug this.
My FF can load CKEditor on https://ckeditor.com/.

By the way my users use firefox on Win7 and have some lagging problem sometime during CKEditor loading…

Do you have some way to debug this?

ty

Pascal B