As far as I know the spelling is wrong. Here in western Germany it would be spelled this way: friemeln. Unfortunately I don't know anything about a possible translation. Certainly it can be described as something you do with your hands, an action which takes a longer time because it is difficult to perform. It is not stuck to a specific action, you can friemel a book out of your bag, friemel a piece of chewing-gum under a desk or even 'rumfriemeln' at a computer because you try to repair it.

For some of Frank's examples you can use "to fish s.th. out" - like to fish a book out of a bag. You can pry the piece of gum off the desk. For Thomas' original example maybe "to tear off / to pull off".

The correct spelling is pfriemeln, not friemeln. Northern Germans sometimes have difficulties pronouncing the pf (Fanne, Ferd, Fingsten....)

"pfriemeln" is definitely the right spelling. I would say "pfriemeln" means not only things to do with your hands that are difficult to perform, but it also implies that a lot of small movements are involved. It can either mean you have to be dexterous to da it or have an ironic tone, implying you make a complicated task out of something simple.
But as far as a translation goes I've no idea.

???? Ist der einzige Einfall den ich habe!

laut Duden gibt es beides: friemeln = landsch. für "basteln" und pfriemeln = landsch. für "mit den Fingerspitzen hin und her drehen", "zwirbeln"; ich kenne eher "friemeln" im Sinne von "(an etwas) herumwursteln/wurschteln" (oder ähnliche Bedeutung)

* You’ll probably want to fiddle around with this to get it the way you like.
* Fiddle with the settings to get the effect you want, here are the settings I used:...
* Do a few test passes. Fiddle with the contrast and brightness settings so that the background is white.
* There'll often be a grey point, too, which you can fiddle around with until your image looks nice.

Für pfrimeln im Sinne von rumspielen, rumbasteln u.s.w. geht "to fiddle with / around". Ob das allerdings auch für den besagten Knochen geht kann ich nicht sagen.

To those who said that "pfriemeln" is _definitely_ the right spelling: I am awarer of the fact that "pf" is very often in some areas pronounced as "f", as your examples illuminate, but nevertheless I know this word only spelled with an "f" at the beginning and the Duden says that I'm right (only to "klugscheiß" a bit).

Before you say something like "definitely" you should use all the available sources.

Friemeln, to add something to the discussion is "definitely" a word never used in written german, "as far as I know".

Yes, "friemeln" is definitely the right spelling for "friemeln", but no, it is definitely not the right spelling for "pfriemeln", as "pfriemeln" is spelled with a "p", i.e. "pfriemeln".
Well, or you could just refer to Ursel's comment...

Die Kollegen, die sich mit dem Wort friemeln beschäftigt haben, haben wohl die beste Übersetzung gefunden: fumble

Wie wäre es denn mit "to fiddle" ...

fiddle: Verwendung wie rif in #7.

Nur am Rande:
Was "fummeln" heißt, wissen wir seit Werner Enke ("Zur Sache, Schätzchen"), nämlich "sich unsachgemäß an einer Sache zu schaffen machen". Das ist sicher nicht bedeutungsidentisch mit "friemeln" (nach meinem Sprachgefühl so). Die Erklärung in #4 gefällt mir gut ("a lot of small movements").