Since a while, can't say how long, didn't investigate - DRT doesn't generate pixel test results for tests which have dumpAsText=true set.
With the DRT change in bug 42374, I can reactivate them - and it's already visible that we have regressions *SIGH*.
The svg/dynamic-updates tests want textual results (no render tree dumps) and a pixel test result - w/o pixel tests they're useless, as they are specifically testing dynamic changes of certain attributes/properties + repainting.
Created attachment 62038 [details]
Large patch, as it contains the new pixel test baseline for svg/dynamic-updates.
Comment on attachment 62038 [details]
Landed in r63730.