Mozilla/5.0 (Macintosh; Intel Mac OS X 10.9; rv:28.0) Gecko/20100101 Firefox/28.0 In about:memory, the value for gfx-surface-quartz is negative: 126.66 MB ── canvas-2d-pixels 93.37 MB ── gfx-surface-image -12.51 MB ── gfx-surface-quartz [?!] 0.00 MB ── gfx-textures 164 ── ghost-windows 1,678.02 MB ── heap-allocated 1,719.93 MB ── heap-committed 6.10% ── heap-overhead-ratio 0 ── host-object-urls 0.00 MB ── imagelib-surface-cache 4.55 MB ── js-main-runtime-temporary-peak 12,684 ── page-faults-hard 190,336,174 ── page-faults-soft 2,067.94 MB ── resident 7,668.70 MB ── vsize Happy to provide any other information that could be useful.

Are you able to reproduce this consistently or does it just happen sometimes? Bug 937078 is the same issue, that we see occasionally in our test automation.

I am able to reproduce this consistently, although the exact negative value of course values (at the moment, after restarting FF, it's at -0.04 MB for example). In any case, it appears to be consistently a negative value.

that should read "...of course varies"