How to remove domain substitution in the browser?

Question

Windows

Tell me, please, how to solve the problem:
one fine day, instead of one site (site A), another one (site B) began to open in Firefox. The bottom line is that this is only in Firefox, and the fact that the subdirectories (pages) of site A open as expected, but only the main page is auto-substituted.
How to defeat her? Cookies cleared..

Answer 1

1) clear the browser cache
2) Restart the router, or change DNS to 8.8.8.8
3) Start-run-cmd
ipconfig /flushdns

Answer 2

If the site is not written crookedly, and the htaaccess settings are correct ....
except for cookies, you need to clear the browser cache

Answer 3

Similar to the homepage cache or DNS cache in the browser.
Although there are other options, such as: a proxy in the browser, forced external proxying of the browser, programmed server behavior (a special case - A / B testing), a malicious extension, mitm, etc.