in about:support is your GPU composting enabled under graphics? I would recommend to refresh Firefox on that screen as well. Also you can check "about:performance" to see which extension is fucking you over.

I would recommend using adblock plus instead, as it is many leagues faster than UBlock Origin in Firefox since version 48 I believe (They optimized their code with Mozilla a couple months ago). Just make sure you go into the adblock plus filter preferences and uncheck "Allow some non-intrusive advertising" problem solved.