The problem is some sites does not provide 'name' HTML attribute for form inputs.
The folliwng attribute is required for 'completeFormData' Falkon script, but
if the name is empty, the key (see source code) is also empty, and the expression
(name == key) is always evaluates to true, which leads to misfilling the form.
To fix this we just need to check that 'name' is not empty.
To test enter https://my.amfoss.in/login (enter somethink and click save). There must not be any fields filled.
Unit Tests Skipped
I tested it a little bit, and found out that the problem was not caused by 'name' attribute, but by 'key' - it is empty if an appropriate attribute is not present.
Now to check enter to https://my.amfoss.in/login (enter somethink and click save) and see there is not input
Then you can check it at any site (I choosed phabricator) - it should be autocompleted automatically