• Disable Health Report → about:config → create New boolean value or toggle datareporting.healthreport.uploadEnabled → false + datareporting.healthreport.service.enabled → false → restart browser.

• Customize online privacy + security permissions in Firefox 6/newer:

• global (valid for all web pages): about:permissions → Permissions Manager → change: Store Passwords, Share Location, Set Cookies, Open Pop-up Windows + Maintain Offline Storage → restart browser;
• local (valid for selected web pages only): Tools → Page Info → Permissions tab → change: Load Images, Open Pop-up Windows, Set Cookies, Install Extensions or Themes, Share Location + Maintain Offline Storage.

• Enable Do Not Track (DNT) privacy setting in Firefox 4/newer: Tools → Options → Privacy tab → Tracking → check "Tell web sites I do not want to be tracked" box → click OK or press Enter → restart browser.

• Enable WebGL (3D) video hardware (GPU) acceleration in Firefox 4/5/newer: about:config → change these settings (create them if not present) to (not all settings below exist in all browser versions):

• webgl.msaa-force [boolean] → MultiSample Anti-Aliasing (MSAA) support: true (MSAA always turned on) OR false (allows to turn off MSAA if no video hardware support);
• webgl.msaa-level [integer] → MultiSample Anti-Aliasing (MSAA) level: 0 (MSAA turned off) OR 2 (MSAA level 2x) OR 4 (MSAA level 4x) OR 8 (MSAA level 8x);
• webgl.min_capability_mode [boolean] → false (turns off minimum WebGL capability mode) OR true (turns on minimum WebGL capability mode) for older computers/graphics controllers/video drivers with limited WebGL support;
• webgl.disable_extensions (webgl.disable-extensions) [boolean] → true (disables all WebGL extensions) OR false (enables all WebGL extensions);
• webgl.disabled [boolean] → false (turns on WebGL) OR true (turns off WebGL);
• webgl.enabled [boolean] → true (WebGL turned on for all web sites) OR false (allows to turn on WebGL selectively for specified web sites/servers);
• webgl.force-enabled [boolean] → true (WebGL always turned on) OR false (allows to turn off WebGL if invalid code/access);
• webgl.force_osmesa [boolean] → true [uses Mesa 3D only if using installed Mesa 3D libraries = OSMESA32.DLL (476 KB, right-click to save!)] OR false (if not using Mesa 3D libraries) → more info;
• webgl.osmesalib [string] → type Mesa 3D library full path + file name [only if using installed Mesa 3D libraries = OSMESA32.DLL (476 KB, right-click to save!)]; Windows NTx: %windir%\SYSTEM32\OSMESA32.DLL where %windir% = usually C:\WINDOWS) OR leave blank (if not using Mesa 3D libraries) → more info;
• webgl.prefer-egl [boolean] → true (turns on browser built-in WebGL native platform interface for compatibility with older/slower graphics controller and/or buggy/older graphics driver) OR false (turns off browser built-in WebGL native platform interface to allow better/newer OpenGL ES graphics driver to render WebGL textures);
• webgl.prefer-native-gl [boolean] → true (turns on browser built-in WebGL rendering engine for compatibility with older/slower graphics controller and/or buggy/older graphics driver) OR false (turns off browser built-in WebGL rendering engine to allow better/newer OpenGL ES graphics driver to render WebGL textures);
• webgl.default-no-alpha [boolean] → true (disables alpha compositing support) OR false (enables alpha compositing support);
• webgl.shader_validator [boolean] → true (invalid GPU shader access displays warning messages) OR false (allows all GPU shader access regardless of validation status);
• webgl.verbose [boolean] → true (displays detailed error messages) OR false (does not display error messages unless critical);

→ restart browser.

• Enable video hardware (GPU) layers acceleration in Firefox 4/5/newer: about:config → change these settings (create them if not present) to (not all settings below exist in all browser versions):

• layers.acceleration.force-enabled [boolean] → false (turns off forced video hardware layers acceleration) OR true (turns on forced video hardware layers acceleration);
• layers.acceleration.disabled [boolean] → false (enables video hardware layers acceleration) OR true (disables video hardware layers acceleration);
• layers.acceleration.draw-fps [boolean] → false [disables DirectDraw layers acceleration Frames Per Second (FPS)] OR true [enables DirectDraw layers acceleration Frames Per Second (FPS)];
• layers.async-video.enabled [boolean] → false (disables asynchronous video frame rate independent of monitor refresh rate) OR true (enables asynchronous video frame rate independent of monitor refresh rate);
• layers.prefer-d3d9 [boolean] → false (disables DirectX layers acceleration support) OR true (enables DirectX layers acceleration support);
• layers.prefer-opengl [boolean] → false (disables OpenGL layers acceleration support) OR true (enables OpenGL layers acceleration support);

→ restart browser.

• Enable hardware (GPU) acceleration in Firefox 4/5/newer: Tools → Options → Advanced → General tab → check "Use hardware acceleration when available" box → click OK button → restart browser.

• Enable Direct2D + DirectWrite video hardware (GPU) acceleration in Firefox 4/5/newer only in Windows Vista/2008/7/8/2012 with DirectX 10/11 installed: about:config → change these settings (create them if not present) to (not all settings below exist in all browser versions):

• gfx.direct2d.disabled [boolean] → false (turns on Direct2D hardware GPU rendering engine only in Windows Vista/2008/7/8/2012 with DirectX 10/11) OR true (turns off Direct2D hardware GPU rendering engine for compatibility with older/slower graphics controller and/or Windows 2000/XP/2003 without DirectX 10/11);
• gfx.direct2d.force-enabled [boolean] → true (Direct2D hardware GPU rendering engine always turned on only in Windows Vista/2008/7/8/2012) OR false (allows to turn off Direct2D hardware GPU rendering engine for compatibility with older/slower graphics controller and/or Windows 2000/XP/2003 without DirectX 10/11);
• gfx.font_rendering.cleartype_params.cleartype_level [integer] → negative number (use system or ClearType Tuner rendering defaults: percentage of 100%) OR 0 (disabled) OR positive number (enabled +/- tuned: percentage of 100% = maximum value: 100);
• gfx.font_rendering.cleartype_params.enhanced_contrast [integer] → 0 (disabled: default) OR positive number (enabled +/- tuned: percentage of 100% = maximum value: 100);
• gfx.font_rendering.cleartype_params.gamma [integer] → 0 (disabled: default) OR positive number [enabled +/- tuned = maximum value: 1000 = which corresponds to ClearType default gamma value 1.0];
• gfx.font_rendering.cleartype_params.pixel_geometry [integer] → -1 (ClearType pixel geometry disabled) OR 0 (ClearType pixel geometry default: flat) OR 1 [ClearType pixel geometry enabled: RGB (Red Green Blue) = most common] OR 2 [ClearType pixel geometry enabled: BGR (Blue Green Red) = uncommon];
• gfx.font_rendering.cleartype_params.pixel_structure [integer] → -1 (ClearType pixel structure disabled) OR 0 (ClearType pixel structure default: flat) OR 1 [ClearType pixel structure enabled: RGB (Red Green Blue) = most common] OR 2 [ClearType pixel structure enabled: BGR (Blue Green Red) = uncommon];
• gfx.font_rendering.cleartype_params.rendering_mode [integer] → -1 (ClearType rendering mode disabled) OR 0 (ClearType rendering mode default) OR 1 (ClearType rendering mode enabled: aliased) OR 2 (ClearType rendering mode enabled: GDI Classic) OR 3 (ClearType rendering mode enabled: GDI Natural) OR 4 (ClearType rendering mode enabled: Natural) OR 5 (ClearType rendering mode enabled: Natural Symmetric);
• gfx.font_rendering.directwrite.enabled [boolean] → true (turns on DirectWrite hardware GPU rendering engine only in Windows Vista/2008/7/8/2012 with DirectX 10/11) OR false (turns off DirectWrite hardware GPU rendering engine for compatibility with older/slower graphics controller and/or Windows 2000/XP/2003 without DirectX 10/11);
• gfx.font_rendering.directwrite.use_gdi_table_loading [boolean] → false (turns off software GDI rendering engine to allow using DirectWrite hardware GPU rendering engine in Windows Vista/2008/7/8/2012 with DirectX 10/11) OR true (turns on software GDI rendering engine for compatibility with older/slower graphics controller and/or Windows 2000/XP/2003 without DirectX 10/11);

→ restart browser.