I think the reason accountants and lawyers excessively capitalize has to do with legal documents (contracts and engagement letters) you know, “This contract is between Smith, Evans and Jones (herein after referred to as “the Firm”) and ABC Company, Inc. (hereinafter known as “Company”)…”
So firms got used to capitalizing both words, "Firm" and “Company” (<-- or whatever word you use to describe a client's business like "Bank" or "Agency" or "District" or ... you get the drift) throughout documents, that you started applying that to every type of document including brochures, websites or proposals.
It is grammatically incorrect… as well as giving the "Firm" the appearance of massive self-importance.
Since I'm on the subject, you shouldn't capitalize Partner either. Titles are capitalized when used formally, preceding someone's name such as "President Obama went for a walk." but not "Barack Obama, president of the United States, went for a walk."
So on your bio, you should be "Fred Smith, partner in the tax and estate planning practice area, joined the firm after working with an international [accounting/law] firm where he was a senior manager [or associate]." Note partner/manager/associate isn't capitalized, nor is the practice area, nor is firm.