firefox - Unable to install gnome-shell extensions from https://extensions.gnome.org/ No toggle (ON/OFF) switch - Ask Ubuntu

i unable select/install gnome-shell extensions when visiting https://extensions.gnome.org/ [filter settings: 'compatible with: current version'] described in faq section. searched related posts (in forum), not find helpful information - although several people seem affected similar issues.

• what first comes eye when visiting o.m. domain, application icons , threads appear in pale (i.e. faded) color
• when selecting either of these applications, toggle (i.e. on/off switch) is missing; no pop-up/red banner shown, since gnome-shell integration plugin activated
• remarkably, reviews not loading (i.e. seem continue load forever)
• the 'installed extensions' tab [https://extensions.gnome.org/local/] accessible, empty

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the system/setup using:

• ubuntu (gnome) 16.04.1 lts 64-bit
• kernel vers.: 4.4.0-45
• gnome shell 3.18.5
• gnome-tweak-tool installed
• firefox vers.: 49.0.2
  • the gnome-shell integration plugin enabled ['always activated'; confirmed in 'about:plugins']
  • 'click_to_play' settings disabled(i.e. set false) [in 'about:config']

just exclude putative conflicts, here output of apparmor_status | grep firefox

/usr/lib/firefox/firefox{,*[^s][^h]} /usr/lib/firefox/firefox{,*[^s][^h]}//browser_java /usr/lib/firefox/firefox{,*[^s][^h]}//browser_openjdk /usr/lib/firefox/firefox{,*[^s][^h]}//lsb_release /usr/lib/firefox/firefox{,*[^s][^h]}//sanitized_helper /usr/lib/firefox/firefox{,*[^s][^h]} (2937)  /usr/lib/firefox/firefox{,*[^s][^h]} (3694)  

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i tried repeatedly reload pages/restart firefox/restart gnome-shell/reboot system. no change far.

would highly appreciate ideas might cause issue.

update: circumvented issue installing epiphany browser via sudo apt-get install epiphany. using browser able install shell extensions of interest using web-integrated toggle (all above-mentioned irregularities unobserved).

since extensions locally saved in ...

~/.local/share/gnome-shell/extensions

... removed epiphany , dependent files: sudo apt-get remove epiphany && sudo apt-get autoremove [i reluctant use purge command.].

making blind guess there might have been conflict between (some) firefox (default) configurations , communication between script on https://extensions.gnome.org/local/ gnome-shell?

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ps: in case has issues installing gnome-shell extension 'system monitor' on ubuntu (gnome) 16.04, i.e. silent fail of installation using toggle co-occurrent switch going 'off' position after page-refresh, might need install libgtop2-10 & gir1.2-gtop-2.0code. extension dependent on those, seem not included default in 16.04 lts installation. apparently missing dependencies recognized , installation web-interface fails/is aborted reason. unfortunately not dclearly informed error.