Thanks. Although that didn't get rid of the PaintController errors, it stopped the looping, which made the log manageable.
The log is quite cryptic, but it looks like the crash happens here:
[29112:29168:0317/003725.993994:VERBOSE1:url_filter.cc(359)] Invalid rule: /www\.tichyseinblick\.de\/.+\w+\/\w+\.(gif|jpg|png)/
[29112:29168:0317/003725.994028:VERBOSE1:url_filter.cc(359)] Invalid rule: /www\.nw\.de\/.+\w+\/\w+\.(gif|jpg|png)/
[29112:29168:0317/003725.994088:VERBOSE1:url_filter.cc(359)] Invalid rule: /www\.fanfiktion\.de\/.+\w+\/\w+\.(gif|jpg|png)/
[29112:29168:0317/003725.994128:VERBOSE1:url_filter.cc(359)] Invalid rule: /www\.frag-mutti\.de\/.+\w+\/\w+\.(gif|jpg|png)/
[29112:29168:0317/003725.994154:VERBOSE1:url_filter.cc(359)] Invalid rule: /www\.weser-kurier\.de\/.+\w+\/\w+\.(gif|jpg|png)/
[29112:29168:0317/003725.994185:VERBOSE1:url_filter.cc(359)] Invalid rule: /www\.donnerwetter\.de\/.+\w+\/\w+\.(gif|jpg|png)/
[29112:29130:0317/003726.037608:VERBOSE1:content_verifier.cc(595)] OnFetchComplete hhhfihlmbcifeafjbbjfkclpofddkalf success:1
[29112:29130:0317/003726.039130:VERBOSE1:content_verifier.cc(595)] OnFetchComplete kgogikjfdpdkoedplfagjjcfodbokblg success:1
[29112:29130:0317/003726.043473:VERBOSE1:content_verifier.cc(595)] OnFetchComplete kipjbhgniklcnglfaldilecjomjaddfi success:1
[29112:29130:0317/003726.060958:VERBOSE1:content_verifier.cc(595)] OnFetchComplete mjfdcfnlgkhmadiafkpopgifghhgoaif success:1
[29112:29130:0317/003726.072405:VERBOSE1:content_verifier.cc(595)] OnFetchComplete mmmbddcnnndpbdflpccgcknaaabgldak success:1
[29112:29112:0317/003726.128330:VERBOSE1:top_active_pages.cc(50)] Received history query results.
[29112:29112:0317/003726.128412:VERBOSE1:partner_offer_history_fetcher_composite.cc(55)] Fetched transaction 0, remaining tasks: 1
[29329:1:0317/003726.186601:ERROR:child_thread_impl.cc(858)] Receiver for unknown Channel-associated interface: chrome.mojom.SearchBouncer
[29335:1:0317/003726.208600:ERROR:child_thread_impl.cc(858)] Receiver for unknown Channel-associated interface: chrome.mojom.SearchBouncer
[29112:29112:0317/003726.218161:WARNING:x11_util.cc(1415)] X error received: serial 686, error_code 10 (BadAccess (attempt to access private resource
denied)), request_code 33, minor_code 0 (X_GrabKey)
[29112:29112:0317/003726.218752:WARNING:x11_util.cc(1415)] X error received: serial 687, error_code 10 (BadAccess (attempt to access private resource
denied)), request_code 33, minor_code 0 (X_GrabKey)
[29112:29112:0317/003726.218978:WARNING:x11_util.cc(1415)] X error received: serial 688, error_code 10 (BadAccess (attempt to access private resource
denied)), request_code 33, minor_code 0 (X_GrabKey)
[29112:29112:0317/003726.219024:WARNING:x11_util.cc(1415)] X error received: serial 690, error_code 10 (BadAccess (attempt to access private resource
denied)), request_code 33, minor_code 0 (X_GrabKey)
[29368:1:0317/003726.232408:ERROR:child_thread_impl.cc(858)] Receiver for unknown Channel-associated interface: chrome.mojom.SearchBouncer
[29372:1:0317/003726.307223:ERROR:child_thread_impl.cc(858)] Receiver for unknown Channel-associated interface: chrome.mojom.SearchBouncer
[29377:1:0317/003726.336040:ERROR:child_thread_impl.cc(858)] Receiver for unknown Channel-associated interface: chrome.mojom.SearchBouncer
[29112:29112:0317/003726.341142:VERBOSE1:session_recorder_impl.cc(518)] [initial_context] 861b
[29399:1:0317/003726.357376:ERROR:child_thread_impl.cc(858)] Receiver for unknown Channel-associated interface: chrome.mojom.SearchBouncer
[29755:1:0317/003726.364178:VERBOSE1:sandbox_linux.cc(69)] Activated seccomp-bpf sandbox for process type: renderer.
[29112:29112:0317/003726.394620:VERBOSE1:top_active_pages.cc(50)] Received history query results.
[29149:29156:0317/003726.396094:VERBOSE1:network_delegate.cc(32)] NetworkDelegate::NotifyBeforeURLRequest: https://duckduckgo.com/?q=firefox+%22browse
r.tabs.get%22&t=opera&ia=web
[29456:1:0317/003726.418500:ERROR:child_thread_impl.cc(858)] Receiver for unknown Channel-associated interface: chrome.mojom.SearchBouncer
[29763:1:0317/003726.453416:VERBOSE1:sandbox_linux.cc(69)] Activated seccomp-bpf sandbox for process type: renderer.
[29399:1:0317/003726.463551:ERROR:paint_controller.cc(548)] PaintController::FinishCycle() completed
[29458:1:0317/003726.465874:ERROR:child_thread_impl.cc(858)] Receiver for unknown Channel-associated interface: chrome.mojom.SearchBouncer
[29766:1:0317/003726.470674:VERBOSE1:sandbox_linux.cc(69)] Activated seccomp-bpf sandbox for process type: renderer.
[29329:1:0317/003726.514292:ERROR:paint_controller.cc(548)] PaintController::FinishCycle() completed