Mozilla does not have a release version of Firefox 64-bit for Windows. You can either wait for it or use the prerelease version called Developer edition, ftp://ftp.mozilla.org/pub/firefox/nightly/latest-mozilla-aurora/

(removed trailing part to the .exe file - c)

thx if i install this will it delete all my bookmarks and all my add ons ?

Hello can you send me the link again its not working i have fire fox 35.0.1 it's slowing down my laptop need help plz and thx

here are current links: https://www.mozilla.org/en-US/firefox/developer/all/

when I install this will it copy all my things from my old fire fox ?

not by default: Recover lost bookmarks on Firefox Developer Edition

how can I tell if the sync is working or not ?

System Requirements

Please note that while the 32-bit and 64-bit versions of Windows Vista and Windows 7 can be used to run Firefox, only 32-bit builds of Firefox are supported at this time.

64-Bit version of stable FireFox for windows is available, however no download link for the 64-Bit version is supplied as of yet ?

There is no Win64 for Firefox Release yet as to why there is no easy to find download links for Release.

While there has been Win64 being built of the Beta channel for Firefox 37.0b# and 38.0b# it did not continue to Release either time. The Windows Firefox 38.0.x release is still 32-bit as you can see at www.mozilla.org/firefox/all

If you really want to use Win64 builds then there is the 38.0.5b# beta builds currently at https://www.mozilla.org/firefox/beta/all/ as current build is 38.0.5b2. Note this will put you on Beta channel so if you want Release again, the easy way to change is to install the current Release.

The 39.0b1 is not scheduled until May 26 (normally first Beta would have been out about time of Release) due to the extra 35.0.5 branch builds at moment which will be kinda like that Firefox 33.1 10th Anniversary version back in November even though Firefox was actually over twelve years old at time.

Actually would not be surprised if it is not until Firefox 41.0 at earliest for Win64 Release. https://wiki.mozilla.org/Firefox/win64