Reliable 3rd-party source for downloading softwares for Macbook?
The most reliable place for downloads for Mac is the App Store.

It is already installed on your Mac (just click on the top left Apple icon)

Also, you do not have to go to http://www.filehippo.com/mac to get Firefox or Chrome.

If not available at App Store, I usually go directly to the Developer web site to get the download.