Help with mod_rewrite.c error

Hello everyone,
I have a website https://flippinghousessandiego.com which is built on a premium theme.
After i updated the wordpress to the current version, i cant reach flippinghousessandiego.com/wp-admin through Mozilla Firefox. It displays this error:

Not Acceptable!

An appropriate representation of the requested resource could not be found on this server. This error was generated by Mod_Security.

Remember that this error only displays on firefox, i can easily access the admin side with chrome and everything works perfectly on other browsers. The website even works fine at Firefox but when i try to reach wp-admin it gives me this error. Whats the matter? How can i solve this?

Regards
Talha Imam
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