When Firefox detects your computer graphic card doesn’t support hardware acceleration, the browser turns it off by default. You can check whether Firefox browser using hardware acceleration or not by visiting ‘Graphics’ section in about:support page.

Till now Mozilla has used its 2D graphics engine, Azure, which has multiple backends enabled for Windows such as Direct 2D, Direct2D 1.1, Skia and Cairo. The Firefox browser vendor has decided to use Google’s Skia as the default software rendering backend for content on Windows from Firefox 52 onwards when Direct2D is not in use.

firefox-52-skia-content-on-windows-enabled-by-default

With this change, if you visit about:support page, you can notice the ‘Diagnostics’ section under ‘Graphics’ displays both AzureCanvasBackend and AzureContentBackend report skia has been used as backend. With Skia enabled, font rendering gets somewhat better when compared without it when HWA is off.

Behind the scenes, Mozilla changes below the preferences values to Skia, Cairo.

gfx.canvas.azure.backends = skia,cairo
gfx.content.azure.backends = skia,cairo

Check this bug link – Bug 1007702 – (skia-windows) Enable skia content on Windows by default when not using D2D,– for more details.