Background The unprecedented outbreak of the Coronavirus disease (COVID-19) resulted in numerous psychological consequences among young Mauritians. Prominently, an increase in Facebook usage during the pandemic was observed which could influenced the mental well-being of Facebook users. Objective The current study sought to explore how the pattern of use, as well as the purpose of Facebook usage, could impact the mental well-being of young Mauritian adults, before, during and after the pandemic-mediated confinement. Method A cross-sectional approach using a sample of 378 young adults was chosen with a self-administered questionnaire shared through online mediums. The instrument consisted of a combination of validated scales and self-developed items. Results The findings revealed a radical proliferation of social media (91%) through a self-perceived dependency for its informative purpose and related addiction; as well as an evolution of adverse psychological effects characterized by a spectrum of feelings such as restlessness and lowered self-esteem. Higher scores of depressive symptoms were observed during the confinement period (10.05 ± 0.13) as opposed to pre- (0.31 ± 0.79) and post- (0.38 ± 0.09) temporal zones. The lowest scores of mental well-being were noted during the confinement period (0.77 ± 1.8) as compared to pre-confinement (6.56 ± 1.42) and a remarkable recovery was observed post the confinement phase (6.68 ± 1.32). Changes in emotional states were also identified as important predictors of Facebook addiction (χ2(1) = 94.54, p < 0.001) with 48.8% of the variation in the reported addiction behavior matched with 92.6% of perceived addictive characteristics. Conclusion Facebook dependency during the lockdown period was paired with a number of adverse psychological effects among young Mauritians; effects which were likely associated with the frequency and purpose of Facebook use during the pandemic.