HB 1577 expands eligibility for the full exemption from ad valorem taxation on the residence homestead of a surviving spouse of a first responder killed or fatally injured in the line of duty. The bill includes federal immigration enforcement agents, customs and border protection officers, and deportation officers within the definition of "first responder." Additionally, it clarifies that surviving spouses of these federal personnel must have been residents of Texas at the time of the first responder’s death to qualify for the exemption, provided they have not remarried. This change applies to tax years beginning January 1, 2026, and the act takes effect on the same date.