Victor Orta's determination to land the €15m man is seen as somewhat of a rescue mission, for a player who struggled to take the form and freedom he showed at Benito Villamarín Stadium to Camp Nou.
Elland Road and the Premier League represent a fresh start for Firpo, still only 24.
This move has to make sense in a way his last one, a 2019 £16.5m transfer to the Spanish giants, did not.
"I first noticed him in late 2017, early 2018, with a very good Betis B team. He stood out," said David Cartlidge, ESPN UK editor and former Spanish football writer for FourFourTwo.
"Moving to Barça so soon made no sense to me, a lot of these kids make the switch too early. He needed another year with Betis in my opinion."
In the green and white of Betis, for the guts of two seasons leading up to his departure, he looked at home, according to Spanish football journalist Guillem Balague.
"When he was at Betis he looked like a very happy, brave full-back who went forward very often, in a team who were playing three at the back," Balague told the YEP.
"It really suited him. He defended decently but attacked much better."
It was difficult to make a home for himself with his new club, however. Behind Spanish international veteran Jordi Alba in the pecking order, Firpo's opportunities were limited.
Cartlidge saw no signs that frustration was getting the better of Firpo's professionalism but the situation was less than ideal and there was a knock-on effect.
"He's been incredibly professional the entire time," he said.
"I think the managerial instability didn't help, plus Quique Setién [former Betis manager] not really using him, despite being a favourite at Betis, was odd.
"It knocked his confidence and when he did get a chance he didn't seem up to speed."
Balague suggests that being a Barcelona player and all that entails was not quite right for Firpo, who in turn was not quite right for Barça.
"Obviously at Barcelona the stakes go much higher," he said.
"He doesn't seem to be for that special style at Barcelona, which requires perfect timing of your runs, understanding you sometimes have to be a central midfielder, understand the positional game. He just didn't do that very well.
"I think he was taken aback by the responsibilities and the weight of being at Barcelona, but he's a good enough full-back to play regularly at some point. At the level he showed at Barcelona he shouldn't be a starter, but at the level he showed at Betis he should."
Dan Altman, founder of data platform smarterscout says Firpo's numbers at Betis marked him out as an aggressive defender who recovered the ball a lot, but a poor tackler and a mediocre overall defender when compared with Premier League standards.
At Barcelona, he was a willing but not overly effective defender.
"As a leftback at Barcelona in 2019-20, Junior Firpo was prolific in trying to disrupt moves by the opposition, but his lack of skill as a tackler made him somewhat ineffective in doing so," said Altman.
"He also didn't recover many balls, so his overall defending stats were middling at a Premier League standard. While his skill in aerial duels in open play was pretty good for La Liga, he might find the aerial game more challenging in England – especially on dead balls, where he was much less effective."
The good news for Leeds is that Firpo's areas for improvement are all things that can be and are highly likely to be improved by head coach Marcelo Bielsa.
His track record of developing players is world renowned and Gjanni Alioski, Firpo's left-back predecessor whose contract with Leeds expired last week, is as good a case study as any.
The North Macedonian international improved his defensive capabilities under Bielsa, to the point where he arguably performed his best as a left-back in a late 2020/21 season spell that saw Leeds come up against 'big six' opposition.
Firpo already has the attacking bent that Bielsa likes in a full-back. The rest he can work on.
"What he has is a free spirit, in a way," said Balague.
"He is better offensively than defensively. He has to develop more discipline. When he defends he makes mistakes which are basic, body positioning at times, how he reacts to losing the ball, which can be corrected.
"He drives with the ball very well, he's better at driving with the ball than trying to attack teams who are defending compact. He does it all the time, he insists and insists, so he's got a good mentality."
If he's in the mood, as any player has to be to stand a chance of starting for Bielsa, Cartlidge can see an ideal signing for Leeds.
"From a system point of view he works, because of how Leeds play with their full-backs," he told the YEP.
"Junior has the speed and fitness levels to cover the entire flank, press high, combine with attackers.
"He's going to be especially influential on the break.
"If he recaptures the spirit with which he played at Betis with then he'll be a huge success
"That's the first task, getting him in that mood again."