browser-keyboard does not work

[kq01526]

@sayfullin :

browser-keyboard does no longer seem to work on Firefox and Chrom(e)(ium).

When installing it on Firefox 50, the options page appears and the following error messages are shown on the top of the options page (even though an Internet connection is available):

Connection Error: make sure that Internet is enabled and click 'Save'
Select at least one language again
Connection Error: make sure that Internet is enabled and click 'Save'

And all options are unseleted.

And browser-keyboard does not appear at all when selecting a text field for example.

Similar on Chrom(e)(ium) 55:

After the installation, the options page appears and there are no error messages and everything appears to be fine from the options page, but browser-keyboard does not appear at all when selecting a text field for example.

So, it looks like it doesn't work at all.

Tested on Windows and Linux.

What could be causing this?