The best of the current options is to use the latest version of
exuberant ctags (which has a new C++ parser) to generate both
declaration and definition tags.

gtags works to some extent and provides additional information about the
function signatures but the C++ parser is not accurate and misses scope
information.  gtags can be used with the ctags parser which is effective
but looses the primary advantage of gtags being able to provide function
signatures so support has been switched-off by default.

ebrowse does not appear to be very useful for traversing the OpenFOAM
class tree and the support has been switched-off by default.