hi, this should still be the default behaviour. could you enter about:config into the firefox address bar (confirm the info message in case it shows up) & search for the preference named browser.sessionstore.restore_on_demand. check that this preference is set to true.

browser.sessionstore.restore_on_demand is set on true, but the tabs are loading and videos playing automatically on startup. This also happens on both of my computers.

can you try to refresh firefox and see if this is making a difference?

That worked! Thank you!

Refreshing firefox..... what a hopeless answer. Why in the world would anyone want to reset all his options to the defaults? (easier is creating a new "vanilla" profile.) There has to be something more specific that would resolve this issue.

You can check whether this is caused by one of the installed extensions if the pref settings are correct.

Start Firefox in Safe Mode to check if one of the extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) or if hardware acceleration is causing the problem.

• switch to the DEFAULT theme: "3-bar" menu button or Tools -> Add-ons -> Appearance
• do NOT click the "Refresh Firefox" button on the Safe Mode start window

• https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode
• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

You can check for problems with preferences.

• http://kb.mozillazine.org/preferences_not_saved
• http://kb.mozillazine.org/resetting_preferences

There is also a restore pref for pinned tabs.

• browser.sessionstore.restore_pinned_tabs_on_demand