There are multiple issues here:
1) Loading the CSS is blocked by the about: protocol handler in firefox (this can be fixed in Ubufox)
2) The about: protocol handler in firefox doesn't support relative URI's (so the css files must be referenced with absolute paths in ubuntu-docs)
3) The ubufox code to assemble the localised offline page URI is not activated anywhere, so the non-localised page always loads (which is easy to fix)
There are multiple issues here:
1) Loading the CSS is blocked by the about: protocol handler in firefox (this can be fixed in Ubufox)
2) The about: protocol handler in firefox doesn't support relative URI's (so the css files must be referenced with absolute paths in ubuntu-docs)
3) The ubufox code to assemble the localised offline page URI is not activated anywhere, so the non-localised page always loads (which is easy to fix)