Probably related to gcc4 recompiles. This is the last WebKit-gtk to work properly with devhelp: WebKit-1.1.0-0.17.svn40351.fc11 The latest one is broken: WebKit-1.1.0-0.20.svn41071.fc11 Unfortunately this updates contains both code updates and a new compiler. Note that nspr has the same problem for gecko (huge 1000 pixels characters).
bug 487844 is the nspr issue, whatever gets decided is the best course of action there probably should be adapted here. (JavaScriptCore/wtf/dtoa.cpp)
*** This bug has been marked as a duplicate of bug 488112 ***