We are working on a Java front end for Firefox mobile. Performance on devices that were marginal at running XUL Firefox mobile is much improved. There were a couple design decisions that made Firefox mobile slow to startup. First it was a testbed for Firefox multiprocess work. Secondly shipping as a full NDK app as complex as Firefox could not compete with Java app startup time due to library unpacking. This was exacerbated on phones that had a poor filesystem such as the Galaxy S.
If you want to give the Java native version a try it can be downloaded from http://nightly.mozilla.org/ It will require you to enable installing of non-market apps on your phone.
Adding Flash to Firefox was a considerable amount of work. Adobe and Google rather drastically re-wrote NPAPI. The only documentation on how Flash worked on Android is the Android source. This work represents several hundred person hours to get it working.
TBH Flash support is in the current release version has a pref for flash on 2.2 and 2.3 but the experience is rather poor, hence it being disabled with no UI to enable it. about:config change plugin.disable to false. Judge Flash progress against the Nighty or Aurora builds. The Beta 10 or release 10 builds are not representative of the Flash experience for 11+.
Statistics are no substitute for judgement. -- Henry Clay