Discard Pinned Tabs on Start wót Shajirr

If you set the following flag to discard pinned tabs on browser start in about:config :
browser.sessionstore.restore_pinned_tabs_on_demand - true
it doesn't actually work on Windows due to an unfixed bug, and Firefox loads processes for all pinned tabs anyway, wasting your RAM for no reason.

Even if you already have "Auto Tab Discard" addon, it doesn't work either, doesn't discard pinned tabs.

This extension fixes that by discarding those tabs by itself.

How to check that it actually works (and whether Firefox bug was fixed or not):

• disable the extension
• in about:config check that browser.sessionstore.restore_pinned_tabs_on_demand is set to true
• check if you have any pinned tabs, pin some if needed
• exit the browser, start it again
• go to "about:performance" page, and if you see processes corresponding to the pinned tabs - that means the bug is still present and Firefox still loads them
• enable the extension
• exit the browser, start it again
• go to "about:performance" page, after a brief delay all processes should now be gone

Additionally, if you want a notification displayed when the addon unloads tabs,
you can enable the "notifications" permission by going to about:addons,
selecting this addon, clicking (...) menu on the right -> Manage -> "Permissions and data" tab