I'm not very familiar with RealDownloader but I think Real recently introduced some new software and is not supporting its older add-ons any more.

Are there particular sites where you have this problem, such as YouTube? YouTube has switched most Firefox users to an HTML5 player instead of a Flash-based player, and some recorders may not work with the HTML5 player. To see which one Firefox is using, try right-clicking the player and if you get a short, player-specific context menu, check the last item for a reference to Flash. If you don't see that, it's probably not Flash.

If you need to force the Flash player on YouTube, of course, there's an add-on for that: https://addons.mozilla.org/firefox/addon/youtube-flash-video-player/

By the way, Firefox 37 is known not to be secure; Mozilla discloses security flaws after each new release. Is something holding you back from upgrading to Firefox 39? Please let us know so we can suggest solutions or workarounds.

If you just need an installer, you can use this page: https://www.mozilla.org/firefox/all/ (scroll down to your preferred language)

i downloaded firefox 39 and it still isn't working. The problem started when Firefox automatically updated itself to ver 38. I couldn't download any videos after it updated. I downgraded back to 37, and everything was back to normal. Things were fine for about a week and then Firefox started telling me to upgrade to the lastest version. I clicked the "later" button, but evey time I opened Firefox, I would get the same message- to upgrade. Then my computer started to hang when I tried to start Firefox, with the wait circle spinning round and then disappearing. I would go through this same thing every time I tried to open Firefox for about 2 days. I switched to Google Chrome as a browser for a week and everything was fine.I turned My computer on last Monday,and I couldn't get any browser to come up, just the circle going around and then disappearing.I restarted my computer andstill couldn't open a browser. I started a recovery , setting my recovery point to an Automatic system restore point three weeks before I ever had any problems. The restore point failed, Twice. I ran a Norton virus scan, but didn't come up with any viruses, but Norton did report that the system was becoming unstable,but didn't return any reason. I restarted the computer again and it would not load any icons,just my desktop background.i tried to start Task Manager, but it wouldn't load,just a blank screen.I had to reload Windows(8.1) and the computer is running again. It took 3 days to get all my programs re- installed, but the only thing that isn't working is video downloading through Firefox. I am so disgusted with Firefox. They update every couple of weeks, but don't seem to care about problems that people have when they do upgrade.I dowload videos from all over the Internet for School, and now I have to find a work around again. the same thing happened with Firefox when I had Windows 7.

It sounds like your major issue now is with the 3rd party add-on Real Downloader, not with Firefox directly.

Have you tried getting help from RealNetworks? The company who made the Real Downloader / Real Times.

https://customer.real.com/hc/en-us

Here's a support page for reinstalling on Windows. https://customer.real.com/hc/en-us/articles/204040013