Howto enable flash:
1. Go to URL "about:config"
2. Set filter "plugin"
3. Set "plugin.default_plugin_diabled" and "plugin.disabled" to false
4. Restart Firefox (I'm not sure if this is necessary)
I would wait at least until Adobe release a beta of flash that supports HW acceleration (10.1), until then use the built-in browser. If firefox for mobile has some advantages, they're with the extensions. Which will slow the browser down some more, but if you need an extension that you need to use, mobile firefox is needed.
Also, when trying to use the firefox as a main browser, the user need to remember that the built-in browser opens all links from emails and IMs, but there is an app that allows you to do change that. I think.
It's always good to have an alternative browser available, but is there any danger of interference with microB? Are both using .mozilla? Or are they cleanly separated?
One thing I do like about it is that entering text in fields is much quicker than on MicroB. For example, when entering text into the box to post to this forum, MicroB is a little laggy whereas Firefox isn't. The fit to zoom when you double tap also seems a bit better on Firefox and I do like the left/right swipes to bookmark/see tabs.
On the other hand it is slow rendering pages, the sensitivity is a bit wonky (sometimes it seems to just open links when my finger was nowhere near it) and the way the bookmarks are arranged is a little confusing. But overall, really not bad, I can see me using this for forums where I frequently post.