The most common and most likely answer to this crossword clue is the 11 letter word PARTNERSHIP
P
A
R
T
N
E
R
S
H
I
P
More clues leading to the result PARTNERSHIP
Buddy explains!

The straight part
We know that "Firm’s involvement" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case firm’s involvement = partnership.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does PARTNERSHIP mean?
PARTNERSHIP noun- The state of being associated with a partner.
- An association of two or more people to conduct a business,
- The period when two specific batsmen are batting, from the fall of one wicket until the fall of the next; the number of runs scored during this period,