It's hard to use this browser with WYSIWYG sites like vBulletin, when you have to use the mouse instead of standard keyboard shortcuts. Slows down the user experience.
Firefox and IE use the standard bold and italics code, as does Safari and Chrome.
Hoping you'll consider this change to more standardized use.
With K-Meleon items such as accels (Keyboard shortcuts) are in reach of the end user.
You can edit accel.cfg. Edit -> Configuration -> Accelerators.
p.s. Maybe reconsider Your request. Nobody will change a browser because a mere site
uses a particular shortcut. Use the browsers You mentioned if they give You better user experience on the sites You mentioned.