Argthtjtr

Firefox has a setting "Don't load tabs until selected" (see How do I make Firefox 13 Load All My Tabs on Startup or when Resuming Reload). I like that behaviour.

I am searching for a way to "deload"/deactivate a tab manually for a session (until I reload it).

It should stop all running JavaScript functions and plugins (like Flash). The whole webpage content may disappear until I reload/re-activate the tab, but that is not a requirement. The title has to be displayed as tab label (like it is the case with the startup setting, too).

The workaround would be to restart Firefox and don't switch to the tab I want to be deactivated. This is pretty annoying, of course.

EDIT: Here is what I found so far

• 
  BarTab
  
  
  
  
  • no longer being maintained (see why)
  
  
  
  


• 
  BarTab Lite
  
  
  
  
  • (thanks, @bytebuster)
  
  
  • seems to miss this functionality from BarTab
  
  
  
  


• 
  Dormancy
  
  
  
  
  • experimental; comes with warning that it "may eat your session"
  
  
  
  


• 
  Suspend background tabs
  
  
  
  
  • (thanks, @Greck)
  
  
  • experimental; is not exactly what I'm looking for, but could be an alternative (doesn't disable videso/Flash, though)
  
  
  
  


• 
  Tab Mix Plus
  
  
  
  
  • Feature request: Unload Tab feature
    
  
  
  
  


• 
  Tab Utilites
  
  
  
  
  • (thanks, @bytebuster)
  
  
  • seems to offer this functionality only for automatic unloading
  
  
  • Feature request: Add "unload tab" to tab context menu.
    
  
  
  
  


• 
  UnloadTab
  
  
  
  
  • removed from addons.mozilla.org (who knows why)
  
  
  
  

In one of the links you referenced at Tab Utilities: Feature Request, there is already an answer from the developer (scroll down to comment no. 4) on how to do this. The answer is to:

• Add the Restart Tab item to the context menu.

Why it's called "Restart Tab" and not "Unload Tab", I don't understand, but he says you can just change it if you want. Set:

• 
  extensions.tabutils.menu.context_restartTab.label to "Unload Tab".

By the way, at the moment it only works on tabs that are not selected/focussed. In other words, if you do "Restart Tab" on the currently open tab, it will just reload. You have to switch to another tab, then right-click on the tab you want to unload, and choose "Restart Tab".

Here are the instructions from the developer, I updated them a little:

1. Set browser.sessionstore.max_concurrent_tabs to 0 in about:config. (BarTab Lite or Load Tabs Progressively extension should also work.)
   [ the above is outdated, in current versions of Firefox, go to preferences/options for Tabs, and check "Don't load tabs until selected". ]




2. Unload tabs manually with Restart Tab or Restart All Tabs menuitem.
   [ first you have to make sure the "Restart Tab" item is added to the context menu, in Tab Utilities preferences/options -> Appearance -> Menus -> Tab Context Menu ]




3. Unload tabs automatically after a specified period of inactivity with extensions.tabutils.restartAfter option (minutes).




4. Tag bookmarks with "norestart" to make an auto-unload black list.

All Tabs Helper and Auto Unload Tab do this, among other things.

A workaround is: by forcing the reloading of a tab using CTRL+F5 and stopping it so far (using the cross in URL bar) it may left you (with luck) with a blank page (or almost blank).

There is the extension BarTab Lite X. This is a light extension. Its feature for unloading tab works with recent Firefoxes.

However, better check that unloaded tabs don't mess up Firefox' session restore.

As of December 2018 the Auto Tab Discard addon appears to be a great option.

The source code is available at https://github.com/rNeomy/auto-tab-discard.

If you have e10s enabled, taskkill /f /im plugin-container.exe or your OS equivalent is a pretty easy solution.

Firefox will think the content process has crashed, but that is wrong.

Clicking on a tab will reload it.