Firefighting exposes personnel to intense psychosocial demands that elevate stress, erode well-being, and heighten burnout risk. m-Health tools may offer scalable, low-cost support for emotion regulation and stress coping in operational settings. The aim was to evaluate the short-term effects of a brief m-Health program, on psychological outcomes (emotion regulation, self-efficacy to cope with stress, perceived stress, well-being, and burnout) and biomarkers (cortisol, alpha-amylase) in professional firefighters. A quasi-experimental design with non-probability, accessibility sampling was implemented. Sixty four firefighters (experimental n=32; control n=32; 96.9% men; mean age=44.11, SD=9.13) participated. The experimental group used the m-health tool for one month; the control group followed routine practice. Saliva samples (08:00, end of 24-h shift) and questionnaires were collected at baseline and post-intervention. Normality of post-pre differences was tested (Shapiro-Wilk). Depending on distribution, intra-group changes were analysed with t-tests or Wilcoxon tests; inter-group differences (post-pre) with independent t or Mann-Whitney. Effect sizes were reported (Cohen's d; r). In the experimental group, emotion regulation improved (p=.002, d=0.43), well-being increased (p=.018, d=0.30), emotional exhaustion decreased (p=.014, d=0.37), and total burnout declined (p=.044, d=0.24). Cognitive impairment showed a small-to-moderate effect suggesting improvement. In the control group, small gains emerged in emotion regulation (p=.044, r=0.36) and well-being (p=.002, d=0.50), while three burnout components were stable or slightly worse and total burnout rose marginally. Between-group analyses indicated a greater reduction in total burnout in the intervention group (p=.034, r=0.30). Biomarkers showed no significant between-group effects; morning cortisol remained within expected ranges on average, with a substantial subset >10 ng/mL at both assessments. Findings support the potential of brief m-Health interventions for psychosocial risk mitigation in firefighters, while underscoring limitations of a small, non-random sample, uncontrolled contextual factors (e.g., vacation periods), limited exposure time, and program adherence.