What is it?
Functional hallux limitus is a problem in which the range of motion of the big toe (“hallux”) joint is limited (“limitus”) when the foot is weightbearing (“functional”). The limitation is not there when the foot is up in the air or non-weightbearing. As this joint is extremely important for walking and allowing the body to move forward over the foot, things are going to go wrong if the foot can not move at this joint. Overpronation, a toe out gait, a more flexed knee are just some of the consequences of functional hallux limitus. A hallux rigidus is different in that the range of motion is restricted both on weightbearing and on non–weightbearing.
How to manage it?
This is pretty close to impossible to self-diagnose, let alone self manage!
When to see the doctor?
If you think you have it, then it is probably a good idea to get to the doctor. Padding and/or foot orthotics are often needed to facilitate the motion at the joint to encourage a more normal git.
For more, the two best resources would have to be Podiatry Arena and Podiatry FAQ.