Sorry to hear that you would like to downgrade your Firefox.

To install Firefox, you will first have to save the executable installer file on your computer's hard drive, by clicking the save button. Once that has been done, you can locate the saved file and open it. Once you follow the steps on the installer, it should install over your current version of Firefox and you should then have Firefox 42.0 installed.

Note: Please close all Firefox windows during the installation process.

Warning: Running an out-dated version of Firefox may prevent security and privacy risks. It is strongly recommended that you always run the latest version of Firefox.

Is there any particular reason that you are interested in downgrading your Firefox? Perhaps we can provide you with the appropriate technical support.

For security reasons, it's recommend not to use old versions of Firefox. Mozilla discloses security flaws after each new release.

What problems are you encountering in Firefox 43 that you think will improve with Firefox 42?

I managed to get 42.0 installed.

I use UltiSend with ViralMailProfits to post to safelists very fast and it does not work with firefox 43.0. That's why I wanted to go back to the previous version.

When UltiSend is vetted for Firefox, I will go to the latest version.

Thanks for your help.

Neil

Those addons were probably disabled because the latest version of Firefox requires all addons to be signed by an automated process for security purposes.

Please consider advising the addon developers about this issue so that they can ensure to get it signed as soon as possible.