Bug 1714483 - Force-disable Nvidia FXAA, r=aosmond

While not enabled by default, it is openly exposed in the driver
settings and thus apparently not uncommon. Currently it causes
significant glitches for Firefox HW-WR, but also other text focused
apps (GTK 4).
While this should get fixed in the driver eventually, use the
workaround recommended by Nvidia to force-disable it for now.

Differential Revision: https://phabricator.services.mozilla.com/D125981

gfx/thebes/gfxPlatformGtk.cpp

@@ -126,6 +126,10 @@ gfxPlatformGtk::gfxPlatformGtk() {
     g_signal_connect(gdkScreen, "notify::resolution",
                      G_CALLBACK(screen_resolution_changed), nullptr);
   }
+
+  // Bug 1714483: Force disable FXAA Antialiasing on NV drivers. This is a
+  // temporary workaround for a driver bug.
+  PR_SetEnv("__GL_ALLOW_FXAA_USAGE=0");
 }
 
 gfxPlatformGtk::~gfxPlatformGtk() {