fix: Bottom tab is no longer cut off. ✂️

Remove extra 22px height from .tabbrowser-arrowscrollbox to account for lightweight themes.
Remove 1px height from .tabbrowser-arrowscrollbox that is visible in certain themes (on Mac).
Add a custom rule for Windows to remain at 42px always.

Fixes #238.
Merge pull request #330 from ericawright/fix/tab_cut_off.

skin/light/light.css

@@ -23,10 +23,21 @@
 }
 
 .tabbrowser-arrowscrollbox {
-  height: calc(100vh - 42px);
+  height: calc(100vh - 63px);
   flex: 1 0;
 }
 
+.tabbrowser-arrowscrollbox:not(:-moz-lwtheme) {
+  height: calc(100vh - 41px);
+}
+
+@media (-moz-os-version: windows-xp), (-moz-os-version: windows-vista), (-moz-os-version: windows-win7), (-moz-os-version: windows-win8), (-moz-os-version: windows-win10) {
+  .tabbrowser-arrowscrollbox,
+  .tabbrowser-arrowscrollbox:not(:-moz-lwtheme) {
+    height: calc(100vh - 42px);
+  }
+}
+
 #verticaltabs-box .tabbrowser-arrowscrollbox > scrollbox {
   overflow-y: hidden !important;
 }