This microsummary lets you create a bookmark in Firefox and have its title show your current reputation on stackoverflow.
Install the stackoverflow user reputation microsummary (or view the source.)
To use the microsummary, bookmark your profile page on stackoverflow by double-clicking the star icon in the Location Bar. In the Name dropdown select the Live Title.

In the screenshot below I've placed the created bookmark next to the Help menu.

meta.stackoverflow thread (with more advanced microsummaries!).