In a build pulled this morning (http://hg.mozilla.org/mozilla-central/rev/93260c1e761e) Firefox doesn't remember the zoom level of pages. Even when switching tabs and switching back to a zoomed page the zoom level returns to the default rather than the user-set level. Steps to reproduce: On any page (e.g. this bug report) zoom in or out with Cmd-+ or Cmd--. Switch to another tab. Switch back to the original tab. Expected results: Zoom level remains as set. Actual results: Zoom level is reset to default. This must be a very recent regression since I use customized zoom levels on sites that I visit every day.
Remembering zoom level works fine for me on Windows with this build: http://hg.mozilla.org/mozilla-central/rev/6d56925adfd5
No problems on OS X 10.6.2 with a 64-bit home made build (@/rev/228adabcc071) and the latest official nightly (12/31, @/rev/6d56925adfd5).
I can't reproduce this any more in today's build, from http://hg.mozilla.org/mozilla-central/rev/cb5a303025fe. (N.B. the changeset in comment 0 is wrong, because I took it from about:buildconfig on a build with local changesets applied)