Let's extend bug 1827960's SVG use intervention to apply to thumbnail-capturing processes (which I believe are content processes, at least according to bug 1734021; and they run in the background so users don't get an opportunity to intervene if they go off the rails).

(Linking this to bug 1162698, which is about the problem of runaway thumbnail-generation processes more generally. This bug here may help out a little bit, in preventing one way in which that might happen.)

For folks wanting to test / look-into-this: to get thumbnails to be generated, I think you have to click the gear on the top-right of your new-tab page and enable the slider for "Recent Activity" (and then disable the other sliders if you like, for simplicity). That'll get thumbnails from recently visited pages to get generated.