Extension gone from toolbar
All of my extensions disappeared from the toolbar. They show as installed and active in the app menu, but don't function. Tried reinstalling extensions, same problem. Refreshed FF, reloaded extensions, same problem. Uninstalled, reinstalled FF, reloaded extensions, same problem. Manually synced, same problem. Extensions still appear and function on my other currently accessible computer (Win 7, 32 bit).
Opaite Mbohovái (3)
Do you have the jigsaw puzzle 
icon in the toolbar?
In case it helps: Manage your extensions using the extensions button in the toolbar
This answer from a past support thread may also help: https://support.mozilla.org/gl/questions/1349658#answer-1441260 Firefox Extensions won't show up or work
jscher2000 - Support Volunteer wrote,
In case you use automatic private browsing mode, you'll need to enable each extension to run in private windows. See: Extensions in Private Browsing.
More on "automatic" private browsing mode in the Private Browsing - Use Firefox without saving history article, under the "Can I set Firefox to always use Private Browsing?" section.