Build: Really test on Firefox ESR, new & old

The previous config declared Firefox ESR testing, but the tests were never run
due to clashing names with main Firefox test runs. Apart from fixing that,
backport jquery/jquery#5682 so that both Firefox ESR versions can be downloaded
despite using different compression algorithms.

Ref jquerygh-597
Ref jquery/jquery#5682

Author: mgol

.github/workflows/browser-tests.yml

@@ -12,14 +12,15 @@ env:
 jobs:
   test:
     runs-on: ubuntu-latest
-    name: ${{ matrix.BROWSER }} (${{ matrix.MIGRATE_VERSION }} Migrate)
+    name: ${{ matrix.NAME || matrix.BROWSER }} (${{ matrix.MIGRATE_VERSION }} Migrate)
     strategy:
       fail-fast: false
       matrix:
+        NAME: [""]
         BROWSER: ["chrome", "firefox"]
         MIGRATE_VERSION: ["min"]
         include:
-          - NAME: "Node"
+          - NAME: ""
             BROWSER: "chrome"
             MIGRATE_VERSION: "esmodules"
           - NAME: "Firefox ESR (new)"
@@ -57,7 +58,13 @@ jobs:
 
       - name: Install Firefox ESR
         run: |
-            wget --no-verbose $FIREFOX_SOURCE_URL -O - | tar -jx -C ${HOME}
+            # Support: Firefox <135 only
+            # Older Firefox used to be compressed using bzip2, newer using xz. Try
+            # to uncompress using xz, fall back to bzip2 if that fails.
+            # Note: this will download the old Firefox ESR twice, but it will still work
+            # when the current ESR version starts to use xz with no changes to the code.
+            wget --no-verbose "$FIREFOX_SOURCE_URL" -O - | tar -Jx -C "$HOME" || \
+            wget --no-verbose "$FIREFOX_SOURCE_URL" -O - | tar -jx -C "$HOME"
             echo "PATH=${HOME}/firefox:$PATH" >> "$GITHUB_ENV"
             echo "FIREFOX_BIN=${HOME}/firefox/firefox" >> "$GITHUB_ENV"
         if: contains(matrix.NAME, 'Firefox ESR')