Upcoming Firefox release milestones

September 2025
SMTWTFS
1
2
3
4
5
6
7
8
9
10
11
144 soft Code Freeze starts at 08:00 UTC
12
144 string freeze starts
144 regression testing completed
145 QA request deadline
13
14
15
Merge day
144 b1 GTB
Nightly 145 starts
16
144 b1
17
144 b2 GTB
18
19
144 b3 GTB
SUMO deadline
145 a11y engineering request deadline for Nightly
20
21
22
144 b4 GTB
23
24
144 b5 GTB
25
26
144 b6 GTB
145 build ready for QA
Final deadline for QA’s Feature Test Plan approval
27
28
29
144 b7 GTB
SUMO content localization starts
30

October 2025
SMTWTFS
1
144 b8 GTB
144 QA sign off
2
3
144 b9 GTB
4
5
6
144 go to Build
7
RC
8
9
145 soft Code Freeze starts at 08:00 UTC
10
145 string freeze starts
145 regression testing completed
146 QA request deadline
11
12
13
Merge day
145 b1 GTB
Nightly 146 starts
14
144 Release
145 b1
15
145 b2 GTB
16
17
145 b3 GTB
SUMO deadline
146 a11y engineering request deadline for Nightly
18
19
20
145 b4 GTB
21
Potential mobile 144.0.x
22
145 b5 GTB
23
24
145 b6 GTB
146 build ready for QA
Final deadline for QA’s Feature Test Plan approval
25
26
27
145 b7 GTB
SUMO content localization starts
28
Planned 144.0.x
29
145 b8 GTB
145 QA sign off
30
31
145 b9 GTB

November 2025
SMTWTFS
1
2
3
145 go to Build
4
RC
5
6
146 soft Code Freeze starts at 08:00 UTC
7
146 string freeze starts
146 regression testing completed
147 QA request deadline
8
9
10
Merge day
146 b1 GTB
Nightly 147 starts
11
145 Release
146 b1
12
146 b2 GTB
13
14
146 b3 GTB
SUMO deadline
147 a11y engineering request deadline for Nightly
15
16
17
146 b4 GTB
18
Potential mobile 145.0.x
19
146 b5 GTB
20
21
146 b6 GTB
147 build ready for QA
Final deadline for QA’s Feature Test Plan approval
22
23
24
146 b7 GTB
SUMO content localization starts
25
Planned 145.0.x
26
146 b8 GTB
146 QA sign off
27
28
146 b9 GTB
29
30

December 2025
SMTWTFS
1
146 go to Build
2
RC
3
4
147 soft Code Freeze starts at 08:00 UTC
5
147 string freeze starts
147 regression testing completed
148 QA request deadline
6
7
8
Merge day
147 b1 GTB
Nightly 148 starts
9
146 Release
147 b1
10
147 b2 GTB
11
12
147 b3 GTB
SUMO deadline
148 a11y engineering request deadline for Nightly
13
14
15
147 b4 GTB
16
Potential mobile 146.0.x
17
147 b5 GTB
18
Planned 146.0.x
19
147 b6 GTB
20
21
22
147 b7 GTB
SUMO content localization starts
23
24
25
26
148 build ready for QA
Final deadline for QA’s Feature Test Plan approval
27
28
29
147 b8 GTB
147 QA sign off
30
31
147 b9 GTB

January 2026
SMTWTFS
1
2
3
4
5
147 go to Build
6
RC
7
8
148 soft Code Freeze starts at 08:00 UTC
9
148 string freeze starts
148 regression testing completed
149 QA request deadline
10
11
12
Merge day
148 b1 GTB
Nightly 149 starts
13
147 Release
148 b1
14
148 b2 GTB
15
16
148 b3 GTB
SUMO deadline
149 a11y engineering request deadline for Nightly
17
18
19
148 b4 GTB
20
Potential mobile 147.0.x
21
148 b5 GTB
22
23
148 b6 GTB
24
25
26
148 b7 GTB
SUMO content localization starts
27
Planned 147.0.x
28
148 b8 GTB
148 QA sign off
29
30
148 b9 GTB
31

February 2026
SMTWTFS
1
2
148 b10 GTB
3
4
148 b11 GTB
5
6
148 b12 GTB
149 build ready for QA
Final deadline for QA’s Feature Test Plan approval
7
8
9
148 b13 GTB
10
11
148 b14 GTB
12
13
148 b15 GTB
14
15
16
148 go to Build
17
RC
18
19
149 soft Code Freeze starts at 08:00 UTC
20
149 string freeze starts
149 regression testing completed
150 QA request deadline
21
22
23
Merge day
149 b1 GTB
Nightly 150 starts
24
148 Release
149 b1
25
149 b2 GTB
26
27
149 b3 GTB
SUMO deadline
150 a11y engineering request deadline for Nightly
28

March 2026
SMTWTFS
1
2
149 b4 GTB
3
Potential mobile 148.0.x
4
149 b5 GTB
5
6
149 b6 GTB
150 build ready for QA
Final deadline for QA’s Feature Test Plan approval
7
8
9
149 b7 GTB
SUMO content localization starts
10
Planned 148.0.x
11
149 b8 GTB
149 QA sign off
12
13
149 b9 GTB
14
15
16
149 go to Build
17
RC
18
19
150 soft Code Freeze starts at 08:00 UTC
20
150 string freeze starts
150 regression testing completed
151 QA request deadline
21
22
23
Merge day
150 b1 GTB
Nightly 151 starts
24
149 Release
150 b1
25
150 b2 GTB
26
27
150 b3 GTB
SUMO deadline
151 a11y engineering request deadline for Nightly
28
29
30
150 b4 GTB
31
Potential mobile 149.0.x

April 2026
SMTWTFS
1
150 b5 GTB
2
3
150 b6 GTB
151 build ready for QA
Final deadline for QA’s Feature Test Plan approval
4
5
6
150 b7 GTB
SUMO content localization starts
7
Planned 149.0.x
8
150 b8 GTB
150 QA sign off
9
10
150 b9 GTB
11
12
13
150 go to Build
14
RC
15
16
151 soft Code Freeze starts at 08:00 UTC
17
151 string freeze starts
151 regression testing completed
152 QA request deadline
18
19
20
Merge day
151 b1 GTB
Nightly 152 starts
21
150 Release
151 b1
22
151 b2 GTB
23
24
151 b3 GTB
SUMO deadline
152 a11y engineering request deadline for Nightly
25
26
27
151 b4 GTB
28
Potential mobile 150.0.x
29
151 b5 GTB
30

May 2026
SMTWTFS
1
151 b6 GTB
152 build ready for QA
Final deadline for QA’s Feature Test Plan approval
2
3
4
151 b7 GTB
SUMO content localization starts
5
Planned 150.0.x
6
151 b8 GTB
151 QA sign off
7
8
151 b9 GTB
9
10
11
151 go to Build
12
RC
13
14
152 soft Code Freeze starts at 08:00 UTC
15
152 string freeze starts
152 regression testing completed
153 QA request deadline
16
17
18
Merge day
152 b1 GTB
Nightly 153 starts
19
151 Release
152 b1
20
152 b2 GTB
21
22
152 b3 GTB
SUMO deadline
153 a11y engineering request deadline for Nightly
23
24
25
152 b4 GTB
26
Potential mobile 151.0.x
27
152 b5 GTB
28
29
152 b6 GTB
153 build ready for QA
Final deadline for QA’s Feature Test Plan approval
30
31

June 2026
SMTWTFS
1
152 b7 GTB
SUMO content localization starts
2
Planned 151.0.x
3
152 b8 GTB
152 QA sign off
4
5
152 b9 GTB
6
7
8
152 go to Build
9
RC
10
11
153 soft Code Freeze starts at 08:00 UTC
12
153 string freeze starts
153 regression testing completed
154 QA request deadline
13
14
15
Merge day
153 b1 GTB
Nightly 154 starts
16
152 Release
153 b1
17
153 b2 GTB
18
19
153 b3 GTB
SUMO deadline
154 a11y engineering request deadline for Nightly
20
21
22
153 b4 GTB
23
Potential mobile 152.0.x
24
153 b5 GTB
25
26
153 b6 GTB
27
28
29
153 b7 GTB
SUMO content localization starts
30
Planned 152.0.x

July 2026
SMTWTFS
1
153 b8 GTB
153 QA sign off
2
3
153 b9 GTB
154 build ready for QA
Final deadline for QA’s Feature Test Plan approval
4
5
6
153 b10 GTB
7
8
153 b11 GTB
9
10
153 b12 GTB
11
12
13
153 go to Build
14
RC
15
16
154 soft Code Freeze starts at 08:00 UTC
17
154 string freeze starts
154 regression testing completed
155 QA request deadline
18
19
20
Merge day
154 b1 GTB
Nightly 155 starts
21
153 Release
154 b1
22
154 b2 GTB
23
24
154 b3 GTB
SUMO deadline
155 a11y engineering request deadline for Nightly
25
26
27
154 b4 GTB
28
Potential mobile 153.0.x
29
154 b5 GTB
30
31
154 b6 GTB
155 build ready for QA
Final deadline for QA’s Feature Test Plan approval

August 2026
SMTWTFS
1
2
3
154 b7 GTB
SUMO content localization starts
4
Planned 153.0.x
5
154 b8 GTB
154 QA sign off
6
7
154 b9 GTB
8
9
10
154 go to Build
11
RC
12
13
155 soft Code Freeze starts at 08:00 UTC
14
155 string freeze starts
155 regression testing completed
156 QA request deadline
15
16
17
Merge day
155 b1 GTB
Nightly 156 starts
18
154 Release
155 b1
19
155 b2 GTB
20
21
155 b3 GTB
SUMO deadline
156 a11y engineering request deadline for Nightly
22
23
24
155 b4 GTB
25
Potential mobile 154.0.x
26
155 b5 GTB
27
28
155 b6 GTB
156 build ready for QA
Final deadline for QA’s Feature Test Plan approval
29
30
31
155 b7 GTB
SUMO content localization starts

September 2026
SMTWTFS
1
Planned 154.0.x
2
155 b8 GTB
155 QA sign off
3
4
155 b9 GTB
5
6
7
155 go to Build
8
RC
9
10
156 soft Code Freeze starts at 08:00 UTC
11
156 string freeze starts
156 regression testing completed
157 QA request deadline
12
13
14
Merge day
156 b1 GTB
Nightly 157 starts
15
155 Release
156 b1
16
156 b2 GTB
17
18
156 b3 GTB
SUMO deadline
157 a11y engineering request deadline for Nightly
19
20
21
156 b4 GTB
22
Potential mobile 155.0.x
23
156 b5 GTB
24
25
156 b6 GTB
157 build ready for QA
Final deadline for QA’s Feature Test Plan approval
26
27
28
156 b7 GTB
SUMO content localization starts
29
Planned 155.0.x
30
156 b8 GTB
156 QA sign off

October 2026
SMTWTFS
1
2
156 b9 GTB
3
4
5
156 go to Build
6
RC
7
8
157 soft Code Freeze starts at 08:00 UTC
9
157 string freeze starts
157 regression testing completed
158 QA request deadline
10
11
12
Merge day
157 b1 GTB
Nightly 158 starts
13
156 Release
157 b1
14
157 b2 GTB
15
16
157 b3 GTB
SUMO deadline
158 a11y engineering request deadline for Nightly
17
18
19
157 b4 GTB
20
Potential mobile 156.0.x
21
157 b5 GTB
22
23
157 b6 GTB
158 build ready for QA
Final deadline for QA’s Feature Test Plan approval
24
25
26
157 b7 GTB
SUMO content localization starts
27
Planned 156.0.x
28
157 b8 GTB
157 QA sign off
29
30
157 b9 GTB
31

November 2026
SMTWTFS
1
2
157 go to Build
3
RC
4
5
158 soft Code Freeze starts at 08:00 UTC
6
158 string freeze starts
158 regression testing completed
159 QA request deadline
7
8
9
Merge day
158 b1 GTB
Nightly 159 starts
10
157 Release
158 b1
11
158 b2 GTB
12
13
158 b3 GTB
SUMO deadline
159 a11y engineering request deadline for Nightly
14
15
16
158 b4 GTB
17
Potential mobile 157.0.x
18
158 b5 GTB
19
20
158 b6 GTB
159 build ready for QA
Final deadline for QA’s Feature Test Plan approval
21
22
23
158 b7 GTB
SUMO content localization starts
24
Planned 157.0.x
25
158 b8 GTB
158 QA sign off
26
27
158 b9 GTB
28
29
30
158 go to Build

December 2026
SMTWTFS
1
RC
2
3
159 soft Code Freeze starts at 08:00 UTC
4
159 string freeze starts
159 regression testing completed
5
6
7
Merge day
159 b1 GTB
8
158 Release
159 b1
9
159 b2 GTB
10
11
159 b3 GTB
SUMO deadline
12
13
14
159 b4 GTB
15
Potential mobile 158.0.x
16
159 b5 GTB
17
18
159 b6 GTB
19
20
21
159 b7 GTB
SUMO content localization starts
22
Planned 158.0.x
23
159 b8 GTB
159 QA sign off
24
25
26
27
28
29
30
31

January 2027
SMTWTFS
1
2
3
4
159 b9 GTB
5
6
159 b10 GTB
7
8
159 b11 GTB
9
10
11
159 go to Build
12
RC
13
14
15
16
17
18
19
159 Release
20
21
22
23
24
25
26
Potential mobile 159.0.x
27
28
29
30
31