This is a metabug to track all of the different bugs that reduce memory usage for Fennec. Ideally we want to get it down to running on 256-meg devices without impacting user experience. I'll start by filing separate bugs for the brainstorming items at https://wiki.mozilla.org/Mobile/BostonBrainstorm/ARMv6
Status update: yesterday I tried running a nightly on a Motorola Milestone which is a 256-meg ARMv7 device. (/proc/meminfo actually reported memory less than 256 meg; the first device I have phyiscally seen to do so). I was able to load CNN after starting fennec. The whole time /proc/meminfo was reporting MemFree on the order of 3-4 MiB so the system is still pretty strapped for memory but it does get the job done. We should probably focus on reducing startup memory usage a bit more to alleviate the memory pressure and also profile Fennec startup on that device to see if there's any other things we can do to improve the startup experience which is slower than I would like.
I'm going to close out this bug since we no longer plan on supporting 256-meg devices. 384 megs is the minimum we plan on supporting, and is supported in FF20 and up. We can still work on some of the dependent bugs to further reduce our memory usage, which will help performance on the 384-meg devices, but this meta-bug is no longer needed.