Bugzilla

On further investigation, this is not device dependent, but it only occurs when HTTPS only is enabled, and the initial download request is made on a website that does not support HTTPS and needs pressing the option "continue to HTTP site" in order to initiate the download. 
When the download is resumed and after pausing it fails with:

``
GeckoConsole:  E  [JavaScript Error: "HTTPS-Only Mode: Upgrading insecure request “https://ipv4.download.thinkbroadband.com/512MB.zip” failed. (M6-C14)"]
``


``
AbstractFe...oadService :   E  Unable to complete download for acbd4aae-1197-4800-a892-ef006ebfdefe marked as FAILED
                                                                                                    java.io.IOException: org.mozilla.geckoview.WebRequestError: Request failed, error=0x33, category=0x3
                                                                                                    	at mozilla.components.browser.engine.gecko.fetch.GeckoViewFetchClient.fetch(GeckoViewFetchClient.kt:61)
                                                                                                    	at org.mozilla.focus.engine.ClientWrapper.fetch(ClientWrapper.kt:22)
                                                                                                    	at mozilla.components.feature.downloads.AbstractFetchDownloadService.performDownload$feature_downloads_debug(AbstractFetchDownloadService.kt:686)
                                                                                                    	at mozilla.components.feature.downloads.AbstractFetchDownloadService.performDownload$feature_downloads_debug$default(AbstractFetchDownloadService.kt:667)
                                                                                                    	at mozilla.components.feature.downloads.AbstractFetchDownloadService.startDownloadJob$feature_downloads_debug(AbstractFetchDownloadService.kt:429)
                                                                                                    	at mozilla.components.feature.downloads.AbstractFetchDownloadService$broadcastReceiver$2$1$onReceive$1.invokeSuspend(AbstractFetchDownloadService.kt:182)
                                                                                                    	at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
                                                                                                    	at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:106)
                                                                                                    	at kotlinx.coroutines.internal.LimitedDispatcher.run(LimitedDispatcher.kt:42)
                                                                                                    	at kotlinx.coroutines.scheduling.TaskImpl.run(Tasks.kt:95)
                                                                                                    	at kotlinx.coroutines.scheduling.CoroutineScheduler.runSafely(CoroutineScheduler.kt:570)
                                                                                                    	at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.executeTask(CoroutineScheduler.kt:750)
                                                                                                    	at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.runWorker(CoroutineScheduler.kt:677)
                                                                                                    	at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.run(CoroutineScheduler.kt:664)
                                                                                                    Caused by: org.mozilla.geckoview.WebRequestError: Request failed, error=0x33, category=0x3
                                                                                                    	at org.mozilla.gecko.mozglue.GeckoLoader.nativeRun(Native Method)
                                                                                                    	at org.mozilla.gecko.GeckoThread.run(GeckoThread.java:677)
``

Edited: double posting.