The installer seems to create a version JSON that is incorrect, or at least that the launcher doesn't like.

 

Steps:

1. Move current .minecraft directory out of the way.
2. Launch the official Minecraft launcher, log in, launch the game once and quit.
3. Grab https://files.minecraftforge.net/maven/net/minecraftforge/forge/1.13.2-25.0.26/forge-1.13.2-25.0.26-installer.jar and run it.
4. Notice the installer says it installed successfully.
5. Launch the Minecraft launcher again.
6. Notice that forge doesn't launch and when you edit the profile the version of forge is not there (even though when you look at the profile list it looks right).
7. Notice the crash log.

 

Crash log:

Spoiler

[17:12:49 INFO]: Minecraft Launcher 1.6.89-j (through bootstrap 4) started on linux...
[17:12:49 INFO]: Current time is Feb 18, 2019 5:12:49 PM
[17:12:49 INFO]: System.getProperty('os.name') == 'Linux'
[17:12:49 INFO]: System.getProperty('os.version') == '4.18.0-15-generic'
[17:12:49 INFO]: System.getProperty('os.arch') == 'amd64'
[17:12:49 INFO]: System.getProperty('java.version') == '1.8.0_191'
[17:12:49 INFO]: System.getProperty('java.vendor') == 'Oracle Corporation'
[17:12:49 INFO]: System.getProperty('sun.arch.data.model') == '64'
[17:12:49 INFO]: proxy == DIRECT
[17:12:49 INFO]: Refreshing local version list...
[17:12:49 ERROR]: Couldn't load local version /home/james/.minecraft/versions/1.13.2-forge-25.0.26/1.13.2-forge-25.0.26.json
com.google.gson.JsonSyntaxException: java.net.MalformedURLException: no protocol:
    at com.google.gson.Gson.fromJson(Gson.java:818) ~[launcher.jar:1.6.89-j]
    at com.google.gson.Gson.fromJson(Gson.java:768) ~[launcher.jar:1.6.89-j]
    at com.google.gson.Gson.fromJson(Gson.java:717) ~[launcher.jar:1.6.89-j]
    at com.google.gson.Gson.fromJson(Gson.java:689) ~[launcher.jar:1.6.89-j]
    at net.minecraft.launcher.updater.LocalVersionList.refreshVersions(LocalVersionList.java:46) [launcher.jar:1.6.89-j]
    at net.minecraft.launcher.updater.MinecraftVersionManager.refreshVersions(MinecraftVersionManager.java:60) [launcher.jar:1.6.89-j]
    at net.minecraft.launcher.Launcher$2.run(Launcher.java:177) [launcher.jar:1.6.89-j]
    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [?:1.8.0_191]
    at java.util.concurrent.FutureTask.run(FutureTask.java:266) [?:1.8.0_191]
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [?:1.8.0_191]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [?:1.8.0_191]
    at java.lang.Thread.run(Thread.java:748) [?:1.8.0_191]
Caused by: java.net.MalformedURLException: no protocol:
    at java.net.URL.<init>(URL.java:593) ~[?:1.8.0_191]
    at java.net.URL.<init>(URL.java:490) ~[?:1.8.0_191]
    at java.net.URL.<init>(URL.java:439) ~[?:1.8.0_191]
    at com.google.gson.internal.bind.TypeAdapters$18.read(TypeAdapters.java:448) ~[launcher.jar:1.6.89-j]
    at com.google.gson.internal.bind.TypeAdapters$18.read(TypeAdapters.java:440) ~[launcher.jar:1.6.89-j]
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.read(ReflectiveTypeAdapterFactory.java:93) ~[launcher.jar:1.6.89-j]
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:172) ~[launcher.jar:1.6.89-j]
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.read(ReflectiveTypeAdapterFactory.java:93) ~[launcher.jar:1.6.89-j]
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:172) ~[launcher.jar:1.6.89-j]
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.read(ReflectiveTypeAdapterFactory.java:93) ~[launcher.jar:1.6.89-j]
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:172) ~[launcher.jar:1.6.89-j]
    at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.read(TypeAdapterRuntimeTypeWrapper.java:40) ~[launcher.jar:1.6.89-j]
    at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:81) ~[launcher.jar:1.6.89-j]
    at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:60) ~[launcher.jar:1.6.89-j]
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.read(ReflectiveTypeAdapterFactory.java:93) ~[launcher.jar:1.6.89-j]
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:172) ~[launcher.jar:1.6.89-j]
    at com.google.gson.Gson.fromJson(Gson.java:803) ~[launcher.jar:1.6.89-j]
    ... 11 more
[17:12:49 INFO]: Refreshing remote version list...
[17:12:50 INFO]: Refresh complete.
[17:12:50 INFO]: Loaded 2 profile(s); selected 'portablejim'
[17:12:50 INFO]: Refreshing auth...
[17:12:50 INFO]: Logging in with access token

 

 

Workaround:

1. Edit the version json to put "http://files.minecraftforge.net/maven/" in the url field for forge (corresponding to source code line https://github.com/MinecraftForge/MinecraftForge/blob/1.13.x/build.gradle#L492)
2. With the file saved, re-launch the launcher.
3. Play modded minecraft.

Its working, thanks a lot

The launcher loads it up just fine.

You know you are not young in the minecraft scene when you forget about the new launcher... Sigh.

 

Note for those not getting the hint: If your launcher looks like the one below... you are eligible for a free upgrade to the one Lex posted.