How can I unload a tab manually?

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 [ the above is outdated, in current versions of Firefox, go to preferences/options for Tabs, and check "Don't load tabs until selected".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.

A workaround: Force the tab to reload using CTRL+F5 and stop it quickly (using the cross in the URL bar). It may leave you with a blank page (or almost blank) which consumes little resources.

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

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.