We have been working on an internal proof-of-concept dashboard for Engineering. The page renders several hundred SVG elements on screen. The performance is satisfactory in release (25.0) but demonstrates sluggishness in Nightly (28). The page is available here: https://metrics.mozilla.com/protected/topcat-working Removing the SVG elements mitigates the problem in Nightly.
Does the problem still occur in a recent Nightly? (it might have been bug 923193 that caused the problem which is now backed out)
The problem no longer occurs for me in Nightly. Taras, can you confirm.