Make sure you have an internet connection before you try to enable firebug. The easiest way to reset Firebug and enable it again is by refreshing the web view. You can do this by either re-confirming the url using the address bar or by simply closing and re-opening the preview screen. Then just tap on "Enable Firebug" again using the action button.

Btw, here is an older thread that discusses nearly the same:

If I find a way to have both I'll add it. It would probably be too technical and confusing to users who do not know the internals if I added it as an option.

That's an interesting alternative. The "save to camera roll" function is a good reason to do it that way - although I'd have to find a shorter button title...

Did you try the cursor navigation wheel by the way? 

I once implemented this and tried it out. Unfortunately, it interfered with vertical scrolling (if you disable auto line wrap) and zooming (two- and three-finger swipes were wrongly detected as pinch-to-zoom). So I didn't add this feature to a released version as a consequence.

Thanks for pointing that out. (The refresh button works too)

I have to admit that I haven't thought of this. I'll see if I can add it in an update.

Did you try to add the user name and password to the url? Like this: http://user:password@example.com/