Hello,

The current version of Firefox is version 45, so you are perfectly safe to continue to use that. Version 46 is a beta version (or a test version) that contains some new stuff that will be in the following version of Firefox. It is not really suited for daily use (yet).

Firefox 45 is the current STABLE build. FileHippo is giving you a developer build, Firefox 46 will not be out until April 2016.

Firefox 45.0 was only released on last Tuesday March 8th.

The Firefox 46.0 is currently on the Beta channel with 46.0b1 being the first Beta build. The 46.0b2 is coming. The 46.0b1 has been a bit crash prone for some Windows users especially which may explain why it is not listed on https://www.mozilla.org/firefox/beta/all/ currently and instead has the last Beta build listed at moment which was the now old 45.0b10.

There are four main development channels for Firefox. Release < Beta (b#) < Aurora (a2) < Nightly (a1).

Filehippo certainly misleads people in thinking the latest Firefox is the current Beta build 46.0b1 and lists the 45.0 Release as older on their site.