You can set these prefs in about:config to disable automatic updating in addition to what you've already tried.:
app.update.auto - false
app.update.enabled - false
app.update.silent - false

Firefox 29 and later versions have the Australis interface that looks different than the user interface in Firefox 28 and older versions.

• With the Australis interface the orange Firefox menu button has been replaced by the three bar Firefox Menu button at the far right end of the Navigation Toolbar
  A consequence of this new menu button is that you no longer can hide the Navigation Toolbar
• There is a star like button to the right end of the search bar on the Navigation Toolbar to bookmark the current web page and a "Show your bookmarks" button next to it to open the Bookmarks in a drop down menu
• It is still possible to have the menu bar visible via the right-click context menu on the toolbars to have menus like the the Bookmarks menu

See also:

• https://support.mozilla.org/kb/how-to-make-new-firefox-look-like-old-firefox

• https://support.mozilla.org/kb/common-questions-after-updating-to-new-firefox
• https://support.mozilla.org/kb/learn-more-about-the-design-of-new-firefox

• http://forums.mozillazine.org/viewtopic.php?f=38&t=2824649

You can look at the Classic Theme Restorer extension to restore some functionality that was lost with the arrival of the Australis style in Firefox 29.

• Classic Theme Restorer: https://addons.mozilla.org/firefox/addon/classicthemerestorer/

You can check the settings of the CTR extension via its Options/Preferences button on the "Firefox/Tools > Add-ons > Extensions" page.

Moses and Cor-el, thanks for your efforts. However, Moses, I am working on a Mac and AFAIK about:config is for PCs. Plus, I don't know how to find about:config on the PC I also have and rarely use. Any assistance there would be useful. And, Cor-el, I don't WANT 29. I never want it again. Today, FF was trying to download the update onto my Mac EVEN THOUGH I have used advanced preferences to tell it to "check for updates, but let me choose whether to install" and have also unchecked "automatically update search engines." (Also, Cor-el and Moses, note that there is no right-clicking on a Mac.) I am now going to try telling FF to "never check for updates" in an effort to prevent a "stealth" download of 29. If I can't prevent it from ignoring my preferences, I am going to abandon FF and go to Safari. Do you either of you helpful gentlemen have any further suggestions, particularly Mac-specific suggestions? Thanks again.

PollyZ:

about:config isn't a feature found in Windows. It's a hidden website in Firefox that allows you to change a ton of prefs in Firefox (if you know what you are doing of course)

Please enter about:config into the Firefox address bar and press ENTER. Once there, click the button that says I'll be careful, I promise! Search for the following prefs and set it to false

• app.update.auto
• app.update.enabled
• app.update.silent

OK, THANKS! I went to about:config and saw that those three items were already set to false. So, perhaps my telling it to "never check for updates" was already reflected there. I'll keep you posted, but I am hopeful this does it. I am a bit irked with FF, however. No previous update ever seemed to reduce flexibility/functionality like this one did. Perhaps I just made mistakes, but when the menu button inscrutably disappeared I could make no changes. If I didn't have Time Machine I would have been stuck (perhaps except for what seems the rather major procedure of starting over, and who needs that kind of tsuris? Thanks again, Moses. Polly

See:

• http://kb.mozillazine.org/ui.click_hold_context_menus